assembly_listing_of_the_operating_system_of_the_sinclair_zx80
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; =================================================== ; ; An Assembly Listing of the ROM of the Sinclair ZX80 ; --------------------------------------------------- ; ; ------------------------- ; Last updated: 12-SEP-2002 ; ------------------------- ; ; <font color=#9900FF>Note.</font> This is not the original text file, which was ; written by John Grant in 1979, but a file that ; performs a similar function in that it assembles ; a 4K ROM file that may be used in ZX80 emulators. ; ; The resultant ROM file is identical to the original ; and a comparison between the object code and the original ; is made as part of the process of uploading this file. ; ; It would be desirable that the original file be published but, until such ; time, this file may serve as a poor substitute. ; ; Actually I learn that the complete Assembly Listing was published, with ; "Designer's Annotations", in 1980. Also in that year, appeared "The ZX80 ; Monitor Listing" by Ian Logan, published by LINSAC. ; ; =================================================== #define DEFB .BYTE ; TASM cross-assembler definitions #define DEFW .WORD #define EQU .EQU ; =================================================== ; ; To do justice to the original program it is desirable ; that, while the instructions should not be over ; commented, what is appended should be of high quality. ; ; Send details of any improvements/corrections to ; <a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="6e090b0108082e190b0f1c03011b1a06400a0b030100400d01401b05401d1e0f0300011a060f00051d">[email protected]</a> ; All contributions will be credited. ; ; File incorporates contributions from ; Peter Liebert-Adelt ; ; and borrows from the writings of ; Wilf Rigter, ; Dr Ian Logan, ; Dr Frank O'Hara. ; ; =================================================== .ORG $0000 ; ----------- ; THE <b><font color=#333388>'START'</font></b> ; ----------- <a name="L0000"></a>;; <b>START</b> L0000: LD HL,$7FFF ; top of possible RAM. ; (highest integer is 32767). LD A,$3F ; page before RAM. JP <A href="#L0261">L0261</a> ; forward to RAM-FILL. ; ------------------- ; THE <b><font color=#333388>'ERROR'</font></b> RESTART ; ------------------- <a name="L0008"></a>;; <b>ERROR-1</b> L0008: POP HL ; drop the return address. LD L,(HL) ; fetch the error code after RST 8. BIT 7,(IY+$00) ; test ERR_NR for value $FF (OK) JR <A href="#L0013">L0013</a> ; forward to continue at ERROR-2. ; ------------------------------- ; THE <b><font color=#333388>'PRINT A CHARACTER'</font></b> RESTART ; ------------------------------- <a name="L0010"></a>;; <b>PRINT-A</b> L0010: JP <A href="#L0560">L0560</a> ; jump forward immediately to PRINT-A-2 ; --- ; A continuation of the previous Error restart. <a name="L0013"></a>;; <b>ERROR-2</b> L0013: RET Z ; return if $FF - OK. LD (IY+$00),L ; else set system variable ERR_NR RET ; return. ; --------------------------------------------- ; THE <b><font color=#333388>'COLLECT NEXT CHARACTER OR SPACE'</font></b> RESTART ; --------------------------------------------- ; This will collect any next character including space (zero). <a name="L0018"></a>;; <b>NXT-CH-SP</b> L0018: JR <A href="#L0052">L0052</a> ; forward to CH_ADD+1 ; --- ; This subroutine will collect the character at the current character address ; searching for the next non-space character should the fetched character be ; a space. <a name="L001A"></a>;; <b>get-char</b> L001A: LD HL,($4026) ; get pointer from CH_ADD LD A,(HL) ; fetch addressed character. ; This subroutine tests the current character in the accumulator retrieving ; the next non-space character should the accumulator contain a space <a name="L001E"></a>;; <b>TEST-CHAR</b> L001E: AND A ; test for space (zero). RET NZ ; return if not a space. ;------------------------------------------- ; THE <b><font color=#333388>'COLLECT NEXT VALID CHARACTER'</font></b> RESTART ;------------------------------------------- <a name="L0020"></a>;; <b>NEXT-CHAR</b> L0020: CALL <A href="#L0052">L0052</a> ; routine CH_ADD+1 JR <A href="#L001E">L001E</a> ; loop back to TEST-CHAR until valid ; --- ; This subroutine advances the character pointer and evaluates the following ; expression. ; It is called twice with CH_ADD addressing the '(' character <a name="L0025"></a>;; <b>EVAL-EXPR</b> L0025: CALL <A href="#L0055">L0055</a> ; routine CH_ADD_LP ; --------------------------------- ; THE <b><font color=#333388>'SCANNING-CALCULATOR'</font></b> RESTART ; --------------------------------- <a name="L0028"></a>;; <b>SCAN-CALC</b> L0028: CALL <A href="#L001A">L001A</a> ; routine get-char. LD B,$00 ; set B to zero as a starting ; priority marker. JP <A href="#L09E1">L09E1</a> ; jump forward to SCANNING ; ---------------------------- ; THE <b><font color=#333388>'MAKE BC SPACES'</font></b> RESTART ; ---------------------------- <a name="L0030"></a>;; <b>BC-SPACES</b> L0030: CALL <A href="#L094F">L094F</a> ; routine TEST-ROOM RET NC ; return if not enough room. PUSH BC ; save number of bytes required. JP <A href="#L0CF3">L0CF3</a> ; jump forward to RESERVE ; -------------------------------- ; THE <b><font color=#333388>'MASKABLE INTERRUPT'</font></b> ROUTINE ; -------------------------------- ; <font color=#9900FF>Note.</font> the maskable interrupt is concerned with generating the TV picture, ; one of the main tasks in the ZX80. This requires some understanding of ; how the video hardware interacts with the system and part of the process ; is to present to the Z80 chip a phantom display file in the upper ; unpopulated 32K of memory. This topsy-turvy display file ; executes characters like "HELLO WORLD" as NOP instructions but recognizes ; a newline ($76) as a true HALT instruction. ; The video hardware sniffs the databus and grabs the data as it flies by ; sending it on to the shifting circuits. The I register permanently holds ; $0E. The video circuitry uses this register and the lower six bits of the ; character to index into the character set bitmaps at the end of this ROM, ; at $0E00, and so cobble together a scan-line. ; If bit 7 of the character latch is set, then the serial video data is ; inverted so that any character in the range 127-191 appears as the inverse ; of normal characters 0 - 63. ; For a proper explanation of this system, I recommend Wilf Rigter's ; online documentation, available from several indexed sites. ; I have borrowed a few comments from that file to remind myself of what ; is happening. I have indicated where the Z80 instructions should be ; read in conjunction with Wilf's file by using a double semi-colon. ; On entry, B holds the line number and C the number of the scanline. <a name="L0038"></a>;; <b>MASK-INT</b> L0038: DEC C ;; decrement the scan line counter in register C. JP NZ,<A href="#L0045">L0045</a> ;; JUMP to SCAN-LINE : repeats 8 times for each ;; row of characters in DFILE. POP HL ;; point to the start of next DFILE row DEC B ;; decrement ROW counter RET Z ;; return if zero to SET 3,C ;; load scan line counter with 08 was 00. <a name="L0041"></a>;; <b>WAIT-INT</b> L0041: LD R,A ;; load refresh register with value $DD. EI ;; enable interrupts. JP (HL) ;; jump to execute the NOPs in DFILE ;; terminated by a NEWLINE/HALT instruction. ; --- <a name="L0045"></a>;; <b>SCAN-LINE</b> L0045: POP DE ;; discard return address. RET Z ;; delay (Zero never set) JR <A href="#L0041">L0041</a> ;; back to WAIT-INT above ; ---------------------------------------------- ; THE <b><font color=#333388>'EVALUATE BRACKETED EXPRESSION'</font></b> SUBROUTINE ; ---------------------------------------------- ; This subroutine is used when an opening bracket is encountered to evaluate ; the expression within. It is called from LOOK-VARS when an integral function ; or array is encountered and recursively from within SCANNING when any ; bracketed argument or sub-expression is encountered. <a name="L0049"></a>;; <b>BRACKET</b> L0049: CALL <A href="#L0025">L0025</a> ; routine EVAL-EXPR LD A,(HL) ; fetch subsequent character CP $D9 ; is character a ')' ? JP NZ,<A href="#L08AE">L08AE</a> ; jump to INS-ERR with other characters. ; else continue and get the character after the ')' ... ; --------------------------------- ; THE <b><font color=#333388>'INCREMENT CH_ADD'</font></b> SUBROUTINE ; --------------------------------- <a name="L0052"></a>;; <b>CH_ADD+1</b> L0052: LD HL,($4026) ; fetch character address from CH_ADD <a name="L0055"></a>;; <b>CH_ADD_LP</b> L0055: INC HL ; increment the pointer. LD ($4026),HL ; set system variable CH_ADD LD A,(HL) ; fetch the addressed value. CP $B0 ; is character inverse 'K' RET NZ ; return if not. >> LD ($4004),HL ; set P_PTR system variable BIT 7,(IY+$19) ; test FLAGX - will be set if K-mode JR Z,<A href="#L0055">L0055</a> ; back to CH_ADD_LP if not K-mode L0066: SET 2,(IY+$01) ; update FLAGS set K mode. JR <A href="#L0055">L0055</a> ; back to CH_ADD_LP ; Note there is no NMI routine at L0066. ; --------------- ; THE <b><font color=#333388>'KEY'</font></b> TABLE ; --------------- ; The Key Table is indexed with a key value 1-78. ; ----------------------- ; THE 39 <b><font color=#333388>'UNSHIFTED'</font></b> KEYS ; ----------------------- <a name="L006C"></a>;; <b>MAIN-KEYS</b> L006C: DEFB $3F ; Z DEFB $3D ; X DEFB $28 ; C DEFB $3B ; V DEFB $26 ; A DEFB $38 ; S DEFB $29 ; D DEFB $2B ; F DEFB $2C ; G DEFB $36 ; Q DEFB $3C ; W DEFB $2A ; E DEFB $37 ; R DEFB $39 ; T DEFB $1D ; 1 DEFB $1E ; 2 DEFB $1F ; 3 DEFB $20 ; 4 DEFB $21 ; 5 DEFB $1C ; 0 DEFB $25 ; 9 DEFB $24 ; 8 DEFB $23 ; 7 DEFB $22 ; 6 DEFB $35 ; P DEFB $34 ; O DEFB $2E ; I DEFB $3A ; U DEFB $3E ; Y DEFB $76 ; NEWLINE ED-ENTER DEFB $31 ; L DEFB $30 ; K DEFB $2F ; J DEFB $2D ; H DEFB $00 ; SPACE DEFB $1B ; . DEFB $32 ; M DEFB $33 ; N DEFB $27 ; B ; ---------------------- ; THE 39 <b><font color=#333388>'SHIFTED'</font></b> CODES ; ---------------------- DEFB $0E ; ':' DEFB $D7 ; ';' DEFB $0F ; '?' DEFB $DF ; '/' DEFB $09 ; mosaic $09 DEFB $08 ; mosaic $08 DEFB $06 ; mosaic $06 DEFB $07 ; mosaic $07 DEFB $0B ; mosaic $0B DEFB $02 ; mosaic $02 DEFB $03 ; mosaic $03 DEFB $04 ; mosaic $0A DEFB $05 ; mosaic $04 DEFB $0A ; mosaic $05 DEFB $DB ; 'NOT' DEFB $E0 ; 'AND' DEFB $D5 ; 'THEN' DEFB $D6 ; 'TO' DEFB $72 ; cursor left DEFB $77 ; [ RUBOUT ] DEFB $74 ; [ HOME ] DEFB $73 ; cursor right DEFB $70 ; cursor up DEFB $71 ; cursor down DEFB $DE ; '*' DEFB $D9 ; ')' DEFB $DA ; '(' DEFB $0D ; '$' DEFB $01 ; '"' DEFB $75 ; [ EDIT ] DEFB $E3 ; '=' DEFB $DD ; '+' DEFB $DC ; '-' DEFB $E2 ; '**' DEFB $0C ; uk currency symbol DEFB $D8 ; ',' DEFB $E4 ; '>' DEFB $E5 ; '<' DEFB $E1 ; 'OR' ; ----------------- ; THE <b><font color=#333388>'TOKEN'</font></b> TABLE ; ----------------- <a name="L00BA"></a>;; <b>TKN-TABLE</b> L00BA: DEFB $D4 ; chr$ 212 - the threshold character ; tokens below this are printed using ; the next character DEFB $8F ; '?' + $80 DEFB $81 ; '"' + $80 DEFB $39,$2D,$2A,$B3 ; THEN DEFB $39,$B4 ; TO DEFB $99 ; ; DEFB $9A ; , DEFB $91 ; ( DEFB $90 ; ) DEFB $33,$34,$B9 ; NOT DEFB $92 ; - DEFB $93 ; + DEFB $94 ; * DEFB $95 ; / DEFB $26,$33,$A9 ; AND DEFB $34,$B7 ; OR DEFB $14,$14+$80 ; ** DEFB $96 ; = DEFB $97 ; < DEFB $98 ; > DEFB $31,$2E,$38,$B9 ; LIST DEFB $37,$2A,$39,$3A,$37,$B3 ; RETURN DEFB $28,$31,$B8 ; CLS DEFB $29,$2E,$B2 ; DIM DEFB $38,$26,$3B,$AA ; SAVE DEFB $2B,$34,$B7 ; FOR DEFB $2C,$34,$00,$39,$B4 ; GO TO DEFB $35,$34,$30,$AA ; POKE DEFB $2E,$33,$35,$3A,$B9 ; INPUT DEFB $37,$26,$33,$29 ; ... DEFB $34,$32,$2E,$38,$AA ; RANDOMISE DEFB $31,$2A,$B9 ; LET DEFB $8F ; '?' + $80 DEFB $8F ; '?' + $80 DEFB $33,$2A,$3D,$B9 ; NEXT DEFB $35,$37,$2E,$33,$B9 ; PRINT DEFB $8F ; '?' + $80 DEFB $33,$2A,$BC ; NEW DEFB $37,$3A,$B3 ; RUN DEFB $38,$39,$34,$B5 ; STOP DEFB $28,$34,$33,$39,$2E ; ... DEFB $33,$3A,$AA ; CONTINUE DEFB $2E,$AB ; IF DEFB $2C,$34,$00,$38,$3A,$A7 ; GO SUB DEFB $31,$34,$26,$A9 ; LOAD DEFB $28,$31,$2A,$26,$B7 ; CLEAR DEFB $37,$2A,$B2 ; REM DEFB $8F ; '?' + $80 ; ---------------------- ; THE <b><font color=#333388>'DISPLAY'</font></b> ROUTINES ; ---------------------- ; -> <a name="L013C"></a>;; <b>DISP-1</b> L013C: CALL <A href="#L01AD">L01AD</a> ;; routine DISP-2 ; The initial entry point <a name="L013F"></a>;; <b>KEYBOARD</b> L013F: LD B,$08 ; (7) set counter to 8 <a name="L0141"></a>;; <b>KB-1</b> L0141: DJNZ <A href="#L0141">L0141</a> ; (13,8) and loop back 7 times. (7*13+8) ; "WASTE 99 T-STATES" <a name="L0143"></a>;; <b>KB-2</b> L0143: LD HL,($401E) ; (16) fetch two-byte FRAMES value. INC HL ; ( 6) increment LD ($401E),HL ; (16) and store in FRAMES again. ; now read the keyboard LD HL,$FFFF ; (10) prepare a buffer LD B,$FE ; ( 7) set B to $FE LD C,B ; ( 4) now BC is $FEFE - slightly slower than ; the equally time-critical LD BC,$FEFE (10) ; that is used in the ZX81 ROM. IN A,(C) ; (12) now read port $FEFE the half-row with ; the shift key. ; "START FRAME SYNC" ; START COUNTING OR $01 ; (7) set the rightmost bit so as to ignore ; shift. <a name="L0154"></a>;; <b>EACH-LINE</b> L0154: OR $E0 ; [7] OR 11100000. LD D,A ; [4] transfer to D. CPL ; [4] complement - only bits 4-0 meaningful now. CP $01 ; [7] sets carry if A is zero. SBC A,A ; [4] $FF if $00 else zero. OR B ; [4] $FF or port FE,FD,FB.... AND L ; [4] unless more than one key, L will still ; be $FF if more than one key pressed A ; is now invalid LD L,A ; [4] transfer to L. ; now consider the column identifier. LD A,H ; [4] will be $FF if no previous keys. AND D ; [4] 111xxxxx LD H,A ; [4] transfer A to H ; since only one key may be pressed, H will, if valid, be one of ; 11111110, 11111101, 11111011, 11110111, 11101111 ; reading from the outer column, say Q, to the inner column, say T. RLC B ; [8] rotate the 8-counter/port address. ; sets carry if more to do. IN A,(C) ; [12] read another half-row. ; all five bits this time. JR C,<A href="#L0154">L0154</a> ; [12],(7) loop back, until done, to EACH-LINE ; (658 T-states). ; the last row read is SHIFT,Z,X,C,V for the second time. RRA ; (4) test the shift key - carry reset if ; pressed. <a name="L0168"></a>;; <b>KB-3</b> L0168: RL H ; (8) rotate H to the left picking up the carry. ; giving column values - ; $FD, $FB, $F7, $EF, $DF. ; or $FC, $FA, $F6, $EE, $DE if shifted. ; we now have H identifying the columns and L identifying the row of the ; keyboard matrix. ; This is a good time to test if this is an American or British machine. ; The US machine has an extra diode that causes bit 6 of a byte read from a ; port to be reset. RLA ; (4) compensate for the shift test. RLA ; (4) rotate bit 7 out. RLA ; (4) test bit 6. SBC A,A ; (4) $FF or $00 (USA) AND $18 ; (7) and 24 ADD A,$20 ; (7) add 32 ; gives either 32 (USA) or 56 (UK) blank lines above the TV picture. ; This value will be decremented for the lower border. LD ($4023),A ; (13) place margin in RESULT_hi. ; The next snippet tests that the same raw key is read twice in succession. ; The first time through, the routine uses a character address value, ; which is inappropriate to match against a key value, but the next time ; through it matches the key value it placed there on the first pass. ; Seems to be 713 T-states. ; ; "717 T-STATES SINCE START OF FRAME SYNC, 545 BEFORE END" LD BC,($4026) ; (20) fetch possible previous key value from ; CH_ADD LD ($4026),HL ; (16) put the fresh key value in CH_ADD. LD A,B ; ( 4) fetch high byte. ADD A,$02 ; ( 7) test for $FF, no-key which will set ; carry. SBC HL,BC ; (15) subtract the two raw keys. EX DE,HL ; ( 4) result, possibly zero, to DE. LD HL,$4022 ; (10) now address system variable RESULT. LD A,(HL) ; ( 7) load A from RESULT_lo. OR D ; ( 4) check the OR E ; ( 4) subtraction result. RET Z ; ( 5,11) return if all three zero. >>> ; T-states = 96 so far ; proceed to debounce. The 'no-key' value $FF must be returned five times ; before a new key is accepted above. ; Holding down a key causes the shift counter to be maintained at five. ; The initial state of RESULT is unimportant. LD A,B ; ( 4) fetch hi byte of PREVIOUS key code. CP $FE ; ( 7) sets carry if valid - ; $FD, $FB, $F7, $EF, $DF SBC A,A ; ( 4) gives $FF if pressed or $00 if no-key. LD B,$1F ; ( 7) prepare the shift counter ; (and also the timed delay) OR (HL) ; ( 7) OR with RESULT_lo AND B ; ( 4) limit the count to five set bits. RRA ; ( 4) 'shift' to right LD (HL),A ; ( 7) place result in RESULT_lo DEC B ; ( 4) adjust the delay counter B to thirty. ; t states = 48 ( Total 96+48=144) <a name="L0194"></a>;; <b>KB-4</b> L0194: DJNZ <A href="#L0194">L0194</a> ;; (13,8) wait a while looping to KB-4 ;; equals 13*29+8 = 385 ; "FRAME SYNC ENDS AT NEXT M1" OUT ($FF),A ;; (11) stops the VSYNC pulse LD A,$EC ;; ( 7) the value for R register LD B,$19 ;; there are 25 HALTs including the initial ;; one. LD HL,($400C) ;; point HL to D-FILE the first HALT ;; instruction. SET 7,H ;; now point to the DFILE echo in the ;; top 32K of address space. CALL <A href="#L01AD">L01AD</a> ;; routine DISP-2 LD A,$F3 ;; prepare to set the R refresh register to $F3. INC B ;; increment the line count DEC HL ;; decrement screen address. DEC (IY+$23) ;; decrement RESULT_hi the blank line counter. JR <A href="#L013C">L013C</a> ;; back to display and read ; --- <a name="L01AD"></a>;; <b>DISP-2</b> L01AD: LD C,(IY+$23) ;; load C the col count from RESULT_hi. LD R,A ;; R increments with each opcode until A6 ;; goes low which generates the INT signal. LD A,$DD ;; set the left margin of all other lines. ;; loaded later to R - the incremental refresh ;; register. EI ;; with R set up, enable interrupts. JP (HL) ;; jump to execute the echo DFILE starting with ;; HALT and waits for the first INT to ;; come to the rescue. ; -------------------------- ; THE <b><font color=#333388>'SAVE'</font></b> COMMAND ROUTINE ; -------------------------- ; There isn't a program name involved. ; The routine saves the System Variables, Program Area and BASIC Variables. ; One of the five System commands that cannot be used from within a program. <a name="L01B6"></a>;; <b>SAVE</b> L01B6: POP DE ; discard return address. LD DE,$12CB ; timing value of 5 seconds for leader. <a name="L01BA"></a>;; <b>SAVE-1</b> L01BA: LD A,$7F ; read port $7FFE. IN A,($FE) ; all 16 bits are placed on address bus. RRA ; test for the space key. JR NC,<A href="#L0203">L0203</a> ; forward, if pressed, indirectly to MAIN-EXEC. <a name="L01C1"></a>;; <b>SAVE-2</b> L01C1: DJNZ <A href="#L01C1">L01C1</a> ; delay self-looping to SAVE-2 DEC DE ; decrement LD A,D ; and test OR E ; for zero. JR NZ,<A href="#L01BA">L01BA</a> ; back if not zero to outer delay loop SAVE-1. LD HL,$4000 ; commence saving at start of RAM. <a name="L01CB"></a>;; <b>SAVE-3</b> L01CB: LD DE,$F808 ; register E counts the 8 bits. ; $F8 is first delay. <a name="L01CE"></a>;; <b>EACH-BIT</b> L01CE: RLC (HL) ; spin the actual program byte. SBC A,A ; $FF or $00. AND $05 ; $05 or $00. ADD A,$04 ; $09 or $04. LD C,A ; timer to C. ; a set bit has a pulse longer than ; an unset bit. <a name="L01D6"></a>;; <b>SAVE-4</b> L01D6: OUT ($FF),A ; pulses LD B,$24 ; delay counter. <a name="L01DA"></a>;; <b>SAVE-5</b> L01DA: DJNZ <A href="#L01DA">L01DA</a> ; self loop for delay to SAVE-5 LD A,$7F ; read the space row and hold for later. IN A,($FE) ; also ... LD B,$23 ; another delay counter. <a name="L01E2"></a>;; <b>SAVE-6</b> L01E2: DJNZ <A href="#L01E2">L01E2</a> ; self loop for delay2 to SAVE-6 DEC C ; decrement pulse counter JR NZ,<A href="#L01D6">L01D6</a> ; back while more to SAVE-4. LD B,D ; a terminating delay - D is zero (256). <a name="L01E8"></a>;; <b>SAVE-7</b> L01E8: NOP ; 4 T-states. DJNZ <A href="#L01E8">L01E8</a> ; execute the NOP 256 times. LD D,$FE ; subsequent timing value DEC E ; decrement the 8 counter. JR NZ,<A href="#L01CE">L01CE</a> ; back if more to EACH-BIT. RRA ; test for space key pressed at last test. JR NC,<A href="#L0203">L0203</a> ; forward, if so, indirectly to MAIN-EXEC. CALL <A href="#L01F8">L01F8</a> ; routine TEST-END does not return if at ; the end. >> JR <A href="#L01CB">L01CB</a> ; else back to do another byte. ; --- ; This subroutine is used by both the SAVE and LOAD command routines ; to check when the required area has been completed and to then make an exit ; from the called loop. ; <font color=#9900FF>Note.</font> that for the LOAD command the value of E_LINE is not that at the outset ; of the LOAD command but at the start of the command that saved the section. ; The first bytes to be loaded are the System Variables and E_LINE will be the ; eleventh and twelfth bytes to be loaded. The low byte is read in before the ; high byte so after the low byte is read in, E_LINE is in an indeterminate ; state. Hence E_LINE_hi is incremented at the outset to avoid a premature ; end to loading. <a name="L01F8"></a>;; <b>TEST-END</b> L01F8: INC HL ; increase pointer. EX DE,HL ; LD HL,($400A) ; load HL with E_LINE - the location following ; the variables end-marker. SCF ; force a carry when equal. SBC HL,DE ; trial subtraction. EX DE,HL ; restore pointer. RET NC ; return if more bytes to do. POP HL ; else drop the return address. <a name="L0203"></a>;; <b>JUMP-EXEC</b> L0203: JP <A href="#L0283">L0283</a> ; JUMP forward to MAIN-EXEC. ; <font color=#9900FF>Note.</font> the above jump could be replaced by a relative jump saving one ; instruction byte. A few other direct jumps to this destination could be ; replaced with a series of relative jumps as has been done elsewhere. ; -------------------------- ; THE <b><font color=#333388>'LOAD'</font></b> COMMAND ROUTINE ; -------------------------- ; A System Command to load a program from tape. <a name="L0206"></a>;; <b>LOAD</b> L0206: POP DE ; discard the return address. <a name="L0207"></a>;; <b>LOAD-1</b> L0207: LD DE,$5712 ; set a timing constant. <a name="L020A"></a>;; <b>LOAD-2</b> L020A: LD A,$7F ; read from port $7FFE. IN A,($FE) ; the keyboard row with space. RRA ; test the outer key. JR NC,<A href="#L0203">L0203</a> ; back, if pressed, indirectly to MAIN-EXEC RLA ; cancel the above RRA. RLA ; now do an RLA to read tape signal - bit 7. JR C,<A href="#L0207">L0207</a> ; back without signal to outer loop LOAD-1. DEC DE ; decrement timer LD A,D ; and test OR E ; for zero. JR NZ,<A href="#L020A">L020A</a> ; back if not to inner loop LOAD-2. INC (IY+$0B) ; increment E_LINE_hi to prevent premature ; end after loading E_LINE-lo. ; see TEST-END. LD HL,$4000 ; start of RAM - system variables to be ; overwritten. <a name="L0220"></a>;; <b>LOAD-3</b> L0220: LD E,$08 ; the bit counter for each byte. <a name="L0222"></a>;; <b>LOAD-4</b> L0222: LD A,$7F ; test the keyboard IN A,($FE) ; reading the RRA ; space key. JR NC,<A href="#L024D">L024D</a> ; forward, if space pressed, to LD-ABORT. RLA ; restore to original state. RLA ; now test the tape bit. JR NC,<A href="#L0222">L0222</a> ; back if ???? to LOAD-4 ; start building up a byte. LD C,$94 ; set timing value. The exit value of this ; register determines if a bit was set or unset. <a name="L022F"></a>;; <b>LOAD-5</b> L022F: LD B,$1A ; inner timer <a name="L0231"></a>;; <b>LOAD-6</b> L0231: DEC C ; decrement counter. IN A,($FE) ; read the tape port. RLA ; test the tape bit. BIT 7,C ; test if counter above 127. A set bit. LD A,C ; save in A. JR C,<A href="#L022F">L022F</a> ; back while bit set to LOAD-5 DJNZ <A href="#L0231">L0231</a> ; decrement B counter and loop while not ; zero to LOAD-6. ; <font color=#9900FF>Note.</font> this instruction has no effect on any ; flags. JR NZ,<A href="#L0242">L0242</a> ; forward if C was > $7F (with NC) to LOAD-7 CP $56 ; compare copy of counter to $56 JR NC,<A href="#L0222">L0222</a> ; back if $56-$7F to LOAD-4 <a name="L0242"></a>;; <b>LOAD-7</b> L0242: CCF ; else clear if from above but set carry if ; branching to here. RL (HL) ; rotate the bit into position. DEC E ; decrement the eight counter JR NZ,<A href="#L0222">L0222</a> ; loop back for entire byte. CALL <A href="#L01F8">L01F8</a> ; routine TEST-END quits early at end. JR <A href="#L0220">L0220</a> ; and back to load another byte. ; --------------------------- ; THE <b><font color=#333388>'LOAD ABORT'</font></b> EXIT ROUTE ; --------------------------- ; If the LOAD command has started to load data then a reset is performed. ; If it's still waiting for the leader then rejoin the main execution loop ; after restoring the location of the Edit Line to its correct value. <a name="L024D"></a>;; <b>LD-ABORT</b> L024D: DEC D ; ?? JP P,<A href="#L0000">L0000</a> ; a reset DEC (IY+$0B) ; restore E_LINE_hi to a valid state. JR <A href="#L0203">L0203</a> ; indirect jump to MAIN-EXEC. ; -------------------------- ; THE <b><font color=#333388>'LIST'</font></b> COMMAND ROUTINE ; -------------------------- ; Another System command that can't be used from within a program. <a name="L0256"></a>;; <b>LIST</b> L0256: RES 7,B ; start by making the high byte, ; of an invalid, user-supplied, RES 6,B ; line number within range $00-$3F. ; this invisible mending is inappropriate and it is preferable to tell the ; user of any typos. e.g. LIST 40000 is silently changed to LIST 7232 ; when the user probably meant to type LIST 4000. However space is tight. LD ($4006),BC ; set E-PPC from line number. POP BC ; discard return address. JR <A href="#L0283">L0283</a> ; forward to MAIN-EXEC which produces an ; 'automatic listing'. ; ---------------------------- ; THE <b><font color=#333388>'INITIALIZATION'</font></b> ROUTINE ; ---------------------------- ; A holds $3F, HL holds $7FFF. <a name="L0261"></a>;; <b>RAM-FILL</b> L0261: LD (HL),$01 ; fill location with 1 (null). DEC HL ; decrement address. CP H ; compare address high byte to $3F. JR NZ,<A href="#L0261">L0261</a> ; back, while higher, to RAM-FILL. <a name="L0267"></a>;; <b>RAM-READ</b> L0267: INC HL ; address the next higher location. DEC (HL) ; decrement to zero. JR Z,<A href="#L0267">L0267</a> ; back, if successful to RAM-READ. ; else we have encountered first unpopulated RAM location. LD SP,HL ; initialize stack pointer at end. PUSH AF ; place gosub end-marker $3F?? LD A,$0E ; set the I register to $0E to tell LD I,A ; the video hardware where to find ; the character set ($0E00). IM 1 ; select Interrupt Mode 1. LD IY,$4000 ; set IY to the start of the forty system ; variables. ; ----------------------------------------------------------------------------- ; ; --------------------- ; THE <b><font color=#333388>'ZX80 MEMORY MAP'</font></b> ; --------------------- ; ; There are forty ($28) system variables followed by Program area ; These are located at the start of RAM. ; ; +---------+---------+-----------+---+-----------+-----------+-------+-------+ ; | | | | | | | | | ; | SYSVARS | Program | Variables |80h| WKG Space | Disp File | Spare | Stack | ; | | | | | | | | | ; +---------+---------+-----------+---+-----------+-----------+-------+-------+ ; ^ ^ ^ ^ ^ ^ ^ ; $4024 VARS E_LINE D_FILE DF_END SP ; DF_EA ; ; ----------------------------------------------------------------------------- LD HL,$4028 ; set to location after sysvars. LD ($4008),HL ; set the system variable VARS. LD (HL),$80 ; and insert variables end-marker. INC HL ; address the next location. LD ($400A),HL ; set the system variable E_LINE. ; and continue... ; ------------------------- ; THE <b><font color=#333388>'MAIN EXECUTION'</font></b> LOOP ; ------------------------- ; This is the MAIN EXECUTION LOOP that handles the creation and interpretation ; of user input. The various 'subroutines' from this main loop including those ; launched from the Editing Keys Table are really just branches which all ; ultimately jump back to here. Although service routines make use of the ; machine stack, the stack is generally empty and only has one return address ; on it during command execution. <a name="L0283"></a>;; <b>MAIN-EXEC</b> L0283: LD HL,($400A) ; fetch E-LINE LD (HL),$B0 ; insert the character inverse 'K'. INC HL ; address the next location. LD (HL),$76 ; insert a newline. INC HL ; address the next location. LD ($400C),HL ; set D-FILE to start of dynamic display file. LD (IY+$12),$02 ; set DF-SZ to 2 lines. ; -> <a name="L0293"></a>;; <b>AUTO-LIST</b> L0293: CALL <A href="#L0747">L0747</a> ; routine CLS sets a minimal display and ; initializes screen values in registers. EX DE,HL ; LD A,B ; load line value, 23, to A. SUB (IY+$12) ; subtract DF-SZ of lower screen. JR C,<A href="#L02F7">L02F7</a> ; forward if the lower screen is 24 lines ; to ED-COPY. INC A ; allow for a blank line. LD B,A ; place in B line EXX ; switch to preserve line/column values. LD HL,($4006) ; fetch E_PPC the current line number. LD DE,($4013) ; fetch the top line on screen from S_TOP. SBC HL,DE ; subtract the two BASIC line numbers EX DE,HL ; and bring S_TOP to HL. JR NC,<A href="#L02B0">L02B0</a> ; forward if current line >= top line to LIST-1. ADD HL,DE ; else reform the E_PPC value LD ($4013),HL ; and make S_TOP the same. <a name="L02B0"></a>;; <b>LIST-1</b> L02B0: CALL <A href="#L060A">L060A</a> ; routine LINE-ADDR gets the address of the ; BASIC line in HL. LD E,$00 ; signal current line yet to be printed <a name="L02B5"></a>;; <b>LIST-ALL</b> L02B5: CALL <A href="#L04F7">L04F7</a> ; routine OUT-LINE JR C,<A href="#L02B5">L02B5</a> ; loop until upper screen is full to LIST-ALL. DEC E ; test if current line has appeared. JR NZ,<A href="#L02F0">L02F0</a> ; forward to LIST-DONE if current line ; has appeared. ; else the current line has yet to appear. PUSH HL ; else save HL ( ) LD HL,($4006) ; fetch E_PPC - the current line. CALL <A href="#L060A">L060A</a> ; routine LINE-ADDR in DE POP HL ; restore HL AND A ; prepare to subtract. SBC HL,DE ; subtract setting carry. LD HL,$4013 ; address system variable S_TOP JR NC,<A href="#L02D8">L02D8</a> ; forward if E_PPC precedes to LN-FETCH EX DE,HL ; else swap pointers. LD A,(HL) ; pick up high byte. INC HL ; address low byte. LDI ; copy low byte to S_TOP_lo. LD (DE),A ; insert the high byte. <a name="L02D3"></a>;; <b>AUTO-L-J</b> L02D3: JR <A href="#L0293">L0293</a> ; back to AUTO-LIST. ; ------------------------------------ ; THE <b><font color=#333388>'CURSOR DOWN EDITING'</font></b> SUBROUTINE ; ------------------------------------ <a name="L02D5"></a>;; <b>ED-DOWN</b> L02D5: LD HL,$4006 ; address system variable E_PPC ; and continue... ; ---------------------- ; THE <b><font color=#333388>'LN-FETCH'</font></b> SECTION ; ---------------------- <a name="L02D8"></a>;; <b>LN-FETCH</b> L02D8: LD E,(HL) ; INC HL ; LD D,(HL) ; PUSH HL ; EX DE,HL ; INC HL ; increment as starting point CALL <A href="#L060A">L060A</a> ; routine LINE-ADDR CALL <A href="#L03C2">L03C2</a> ; LINE-NO POP HL ; restore hi pointer. ; ---------------------- ; THE <b><font color=#333388>'LN-STORE'</font></b> SECTION ; ---------------------- ; On entry, HL holds E_PPC_hi. <a name="L02E5"></a>;; <b>LN-STORE</b> L02E5: BIT 5,(IY+$19) ; test FLAGX. JR NZ,<A href="#L02F7">L02F7</a> ; forward if INPUT to ED-COPY. LD (HL),D ; insert high byte DEC HL ; DECrement LD (HL),E ; insert low byte ; JR <A href="#L0293">L0293</a> ; back to AUTO-LIST ; -------------------------- ; THE <b><font color=#333388>'LIST-DONE'</font></b> SUBROUTINE ; -------------------------- ; When the listing is complete then the rest of the upper display is blanked, ; to erase what may have been printed during the interim, the display file ; cursor is updated and the current line is printed in the lower screen. <a name="L02F0"></a>;; <b>LIST-DONE</b> L02F0: CALL <A href="#L05C2">L05C2</a> ; CL-EOD clear to end of upper display. LD ($400E),DE ; set lower screen position DF_EA ; to end ; and continue... ; ------------------------------------- ; THE <b><font color=#333388>'LOWER SCREEN COPYING'</font></b> SUBROUTINE ; ------------------------------------- ; This is called. ; When the line in the editing area is to be printed in the lower screen. ; It is by repeatedly printing the line when any key is pressed that the ; cursor for instance appears to move. ; It is called in a similar fashion to animate the input line. <a name="L02F7"></a>;; <b>ED-COPY</b> L02F7: LD (IY+$01),$01 ; set FLAGS leading space allowed LD HL,($400A) ; E_LINE CALL <A href="#L07BE">L07BE</a> ; routine MAIN-G checks syntax of line. LD DE,($400E) ; fetch start of lower screen from DF_EA LD B,(IY+$12) ; fetch lines in lower screen from DF_SZ LD C,$01 ; set column to 1 ; to print an initial newline for gap? EXX ; LD HL,($400A) ; fetch start of edit line from E_LINE CALL <A href="#L0512">L0512</a> ; routine OUT-LINE-2 prints characters starting ; with the individual digits of line number. JR C,<A href="#L031D">L031D</a> ; forward with success to LINE-DONE ; else there wasn't enough room in lower screen for line. LD HL,$4012 ; address DF_SZ the Display Size for ; the lower screen. INC (HL) ; increment it. LD A,$18 ; load A with 24 decimal. CP (HL) ; compare to DF-SZ JR NC,<A href="#L02D3">L02D3</a> ; indirect jump back to AUTO-LIST ; if no greater than 24 lines. LD (HL),A ; else limit to 24 lines. <a name="L031D"></a>;; <b>LINE-DONE</b> L031D: CALL <A href="#L05C2">L05C2</a> ; routine CL-EOD clears to the end of lower ; screen CALL <A href="#L013F">L013F</a> ; routine KEYBOARD gets key values in BC. ; now decode the value SRA B ; sets carry if unshifted (bit 7 remains set) SBC A,A ; $FF unshifted, else $00 OR $26 ; $FF unshifted, else $26 LD L,$05 ; there are five keys in each row. SUB L ; set the starting point <a name="L032B"></a>;; <b>KEY-LINE</b> L032B: ADD A,L ; add value 5 (or 1) SCF ; carry will go to bit 7 RR C ; test C (which has 1 unset bit identifying row) JR C,<A href="#L032B">L032B</a> ; back if carry to KEY-LINE ; if only one key pressed C should now be $FF. INC C ; test for $FF JR NZ,<A href="#L02F7">L02F7</a> ; back if multiple keys to ED-COPY ; the high byte of the key value identifies the column - again only one bit is ; now reset. LD C,B ; transfer to B DEC L ; test if this is first time through LD L,$01 ; reduce increment from five to one. JR NZ,<A href="#L032B">L032B</a> ; back if L was five to KEY-LINE ; The accumulator now holds a key value 1-78 decimal. LD HL,<A href="#L006C">L006C</a> - 1 ; location before the MAIN-KEYS table ($006B) ; the index value is 1 - 78. LD E,A ; code to E (D is zero from keyboard) ADD HL,DE ; index into the table. LD A,(HL) ; pick up the letter/number/. BIT 2,(IY+$01) ; test FLAGS K-MODE ? JR Z,<A href="#L034D">L034D</a> ; skip forward if not ADD A,$C0 ; add 192 decimal ; e.g. 'A' 38d + 192 = 230 (LIST) CP $E6 ; compare to 'LIST' JR NC,<A href="#L034D">L034D</a> ; skip forward if command tokens to EDC-2. LD A,(HL) ; else load A from HL again ; (numbers and symbols) <a name="L034D"></a>;; <b>EDC-2</b> L034D: CP $C0 ; set the overflow flag for editing key $70-$77 JP PE,<A href="#L035E">L035E</a> ; forward with range $40 - $7F to ED-KEYS LD HL,($4004) ; else fetch keyboard cursor from P_PTR LD BC,$0001 ; one space required. CALL <A href="#L05D5">L05D5</a> ; routine MAKE-ROOM makes room at cursor. ; note HL - first, DE - LAST LD (DE),A ; and insert the keyboard character. <a name="L035C"></a>;; <b>EDC-JR</b> L035C: JR <A href="#L02F7">L02F7</a> ; loop back to ED-COPY ; ----------------------------- ; THE <b><font color=#333388>'EDITING KEYS'</font></b> SUBROUTINE ; ----------------------------- <a name="L035E"></a>;; <b>ED-KEYS</b> L035E: LD E,A ; transfer code to E. ; (D holds zero from 'keyboard') LD HL,<A href="#L0372">L0372</a>-$70-$70; theoretical base of ED-K-TAB $0292 ADD HL,DE ; index twice ADD HL,DE ; as a two-byte address is required. LD C,(HL) ; low byte of routine. INC HL LD B,(HL) ; high byte of routine. PUSH BC ; push routine address to stack. LD HL,($4004) ; set HL to cursor from P_PTR RET ; jump to routine. ; Note the stack is empty. ; --------------------------------------------- ; THE EDITING <b><font color=#333388>'DELETE ONE CHARACTER'</font></b> SUBROUTINE ; --------------------------------------------- <a name="L036C"></a>;; <b>ED-DEL-1</b> L036C: LD BC,$0001 ; one character JP <A href="#L0666">L0666</a> ; routine RECLAIM-2 ; ------------------------ ; THE <b><font color=#333388>'EDITING KEYS'</font></b> TABLE ; ------------------------ <a name="L0372"></a>;; <b>ED-K-TAB</b> L0372: DEFW <A href="#L03A9">L03A9</a> ; ED-UP $70 DEFW <A href="#L02D5">L02D5</a> ; ED-DOWN $71 DEFW <A href="#L0382">L0382</a> ; ED-LEFT $72 DEFW <A href="#L0387">L0387</a> ; ED-RIGHT $73 DEFW <A href="#L03B9">L03B9</a> ; ED-HOME $74 DEFW <A href="#L03CB">L03CB</a> ; ED-EDIT $75 DEFW <A href="#L0408">L0408</a> ; ED-ENTER $76 DEFW <A href="#L0395">L0395</a> ; ED-DELETE $77 ; ------------------------------------ ; THE <b><font color=#333388>'CURSOR LEFT EDITING'</font></b> SUBROUTINE ; ------------------------------------ <a name="L0382"></a>;; <b>ED-LEFT</b> L0382: CALL <A href="#L039E">L039E</a> ; routine ED-EDGE checks that cursor ; not at start without disturbing HL. ; quits early if not possible. >> DEC HL ; move left. DEC HL ; and again for luck. ; ... ; ------------------------------------- ; THE <b><font color=#333388>'CURSOR RIGHT EDITING'</font></b> SUBROUTINE ; ------------------------------------- <a name="L0387"></a>;; <b>ED-RIGHT</b> L0387: INC HL ; move right LD A,(HL) ; pick up the character. CP $76 ; is it newline ? JR Z,<A href="#L03A7">L03A7</a> ; triple jump back to ED-COPY if so. LD (HL),$B0 ; else place inverse cursor there. LD HL,($4004) ; fetch P_PTR LD (HL),A ; and put character there JR <A href="#L035C">L035C</a> ; double jump back to ED-COPY ; ------------------------------- ; THE <b><font color=#333388>'DELETE EDITING'</font></b> SUBROUTINE ; ------------------------------- <a name="L0395"></a>;; <b>ED-DELETE</b> L0395: CALL <A href="#L039E">L039E</a> ; routine ED-EDGE will loop back to ; ED-COPY if no deletion possible >> DEC HL ; decrement position CALL <A href="#L036C">L036C</a> ; routine ED-DEL-1 JR <A href="#L035C">L035C</a> ; back to ED-COPY ; ------------------------ ; THE <b><font color=#333388>'ED-EDGE'</font></b> SUBROUTINE ; ------------------------ <a name="L039E"></a>;; <b>ED-EDGE</b> L039E: LD DE,($400A) ; fetch E_LINE - start of edit line. LD A,(DE) ; pick up first character. CP $B0 ; test for inverse 'K' RET NZ ; return if cursor not at start. POP DE ; else drop the return address. <a name="L03A7"></a>;; <b>EDC-JR2</b> L03A7: JR <A href="#L035C">L035C</a> ; and back to ED-COPY ; ---------------------------------- ; THE <b><font color=#333388>'CURSOR UP EDITING'</font></b> SUBROUTINE ; ---------------------------------- <a name="L03A9"></a>;; <b>ED-UP</b> L03A9: LD HL,($4006) ; E_PPC CALL <A href="#L060A">L060A</a> ; routine LINE-ADDR EX DE,HL CALL <A href="#L03C2">L03C2</a> ; LINE-NO <a name="L03B3"></a>;; <b>ED-LINE</b> L03B3: LD HL,$4007 ; E_PPC_hi JP <A href="#L02E5">L02E5</a> ; to LN-STORE to store new line ; and produce an automatic listing. ; ------------------------ ; THE <b><font color=#333388>'ED-HOME'</font></b> SUBROUTINE ; ------------------------ ; ED-HOME (SHIFT 9) starts the listing at the first line. ; dropped in later ZX computers. <a name="L03B9"></a>;; <b>ED-HOME</b> L03B9: LD DE,$0000 ; start at 'line zero' JR <A href="#L03B3">L03B3</a> ; back to ED-LINE above. ; -------------------------------------- ; THE <b><font color=#333388>'COLLECT A LINE NUMBER'</font></b> SUBROUTINE ; -------------------------------------- <a name="L03BE"></a>;; <b>LINE-NO-A</b> L03BE: EX DE,HL ; bring previous line to HL ; and set DE in case we loop back a second time. LD DE,<A href="#L03B9">L03B9</a> + 1 ; address of $00 $00 within the subroutine ; above. ; -> The Entry Point. <a name="L03C2"></a>;; <b>LINE-NO</b> L03C2: LD A,(HL) ; fetch hi byte of line number AND $C0 ; test against $3F JR NZ,<A href="#L03BE">L03BE</a> ; back to LINE-NO-A if at end. LD D,(HL) ; else high byte to D INC HL ; increase pointer LD E,(HL) ; low byte in E. RET ; return. ; with next line number in DE ; ------------------------- ; THE <b><font color=#333388>'EDIT KEY'</font></b> SUBROUTINE ; ------------------------- ; Pressing the EDIT key causes the current line to be copied to the ; edit line. The two-byte line number is converted into 4 characters ; using leading spaces if the line is less than 1000. Next the 'K' ; cursor is inserted and the rest of the characters are copied verbatim ; into the edit buffer, keywords remaining as single character tokens. <a name="L03CB"></a>;; <b>ED-EDIT</b> L03CB: LD C,$00 ; set column to zero to inhibit a line feed ; while 'sprinting' to the edit line. ; see PRINT-A-2. LD DE,($400A) ; set DE (print destination) to E_LINE EXX ; switch. LD HL,($4006) ; E_PPC current line. CALL <A href="#L060A">L060A</a> ; routine LINE-ADDR CALL <A href="#L03C2">L03C2</a> ; routine LINE-NO LD A,D OR E JP Z,<A href="#L0283">L0283</a> ; back if zero to MAIN-EXEC ; no program. DEC HL ; point to location before CALL <A href="#L06BF">L06BF</a> ; routine OUT-NUM-2 prints line number ; to the edit line (unseen). DEC HL ; point to line number again CALL <A href="#L0624">L0624</a> ; routine NEXT-ONE gets length in ; BC register. INC HL ; point to the INC HL ; first token. DEC BC ; decrease the length DEC BC ; by the same. EXX PUSH DE ; pick up the print position in the EXX ; edit line. POP DE ; and pop it to this set of registers LD A,$B0 ; the inverse 'K' cursor LD (DE),A ; is inserted after line number. INC DE ; address next 'print' location. PUSH HL ; push position within program. LD HL,$0022 ; an overhead of 34d bytes. ADD HL,DE ; add to edit line position ADD HL,BC ; add in length of line. SBC HL,SP ; subtract the stack pointer. JR NC,<A href="#L03A7">L03A7</a> ; back to ED-COPY if not enough ; room to fill edit line. POP HL ; restore program position. LDIR ; and copy it to edit line. LD ($400C),DE ; update D_FILE JP <A href="#L0293">L0293</a> ; jump back to AUTO-LIST ; ------------------------------ ; THE <b><font color=#333388>'ENTER EDITING'</font></b> SUBROUTINE ; ------------------------------ ; This causes the line to be parsed. ; The subroutine then loops back to MAIN-EXEC. <a name="L0408"></a>;; <b>ED-ENTER</b> L0408: LD HL,($4015) ; fetch X_PTR the error pointer. LD A,H ; check that it is OR L ; zero - no error. JR NZ,<A href="#L03A7">L03A7</a> ; double jump back to ED-COPY ; if an error has occurred during ; syntax checking. LD HL,($4004) ; P_PTR CALL <A href="#L036C">L036C</a> ; ED-DEL-1 gets rid of cursor. LD HL,($400A) ; E_LINE LD ($4026),HL ; CH_ADD CALL <A href="#L001A">L001A</a> ; get-char BIT 5,(IY+$19) ; FLAGX input 1/edit 0 JR NZ,<A href="#L043C">L043C</a> ; forward to MAIN-1 if in input mode. ; else the edit line is to be run. CALL <A href="#L0679">L0679</a> ; INT-TO-HL line number to HL' EXX ; switch in set with the line number. LD A,H ; and test OR L ; for zero. JP NZ,<A href="#L04BA">L04BA</a> ; jump forward with a number to MAIN-ADD ; to add a new BASIC line or replacement. ; else must be a direct command. DEC HL ; make the line number DEC HL ; the value minus two. LD ($4002),HL ; and set PPC CALL <A href="#L0747">L0747</a> ; routine CLS EXX ; LD A,(HL) ; fetch first character. CP $76 ; is it just a newline ? JP Z,<A href="#L0283">L0283</a> ; jump back with newline to MAIN-EXEC ; to produce an automatic listing. ; else check syntax and enter <a name="L043C"></a>;; <b>MAIN-1</b> L043C: LD (IY+$00),$FF ; set ERR_NR to no error LD (IY+$01),$88 ; update FLAGS ; set bit 7 - syntax checking off ; set bit 3 - 'K' mode <a name="L0444"></a>;; <b>M-2</b> L0444: CALL <A href="#L07BE">L07BE</a> ; routine MAIN-G parses and executes the line. ; <font color=#9900FF>Note.</font> this causes the value L0447 to be placed ; on the machine stack as a return address. <a name="L0447"></a>;; <b>M-3</b> L0447: CALL <A href="#L0D0A">L0D0A</a> ; REC-EDIT reclaims the edit line LD DE,($4002) ; fetch current line number from PPC LD HL,$4019 ; address FLAGX BIT 5,(HL) ; test FLAGX - input??? JR Z,<A href="#L0458">L0458</a> ; skip if editing to -> RES 5,(HL) ; update FLAGX - signal editing. INC DE ; increase line number so cursor doesn't show. <a name="L0458"></a>;; <b>M-4</b> L0458: BIT 7,(IY+$00) ; check ERR_NR. JR Z,<A href="#L0488">L0488</a> ; forward if an error has occurred. LD HL,$4001 ; address FLAGS system variable BIT 3,(HL) ; test FLAGS - K mode ? RES 3,(HL) ; update FLAGS - set L mode for future anyway. LD HL,($4026) ; fetch character address CH_ADD INC HL ; JR Z,<A href="#L0474">L0474</a> ; forward if not K mode. EX DE,HL ; current line to HL, next char to DE. LD A,H ; fetch high byte of line number. AND $C0 ; test for -2, -1 - direct command. JR NZ,<A href="#L0488">L0488</a> ; forward to MAIN-ERR if so CALL <A href="#L060A">L060A</a> ; routine LINE-ADDR gets address of this line. <a name="L0474"></a>;; <b>M-5</b> L0474: LD A,(HL) ; fetch AND $C0 ; JR NZ,<A href="#L0488">L0488</a> ; at program end ; else pick up the next line number LD D,(HL) ; INC HL ; LD E,(HL) ; LD ($4002),DE ; place in PPC system variable INC HL ; point to first character ; (space or command) LD A,$7F ; test for IN A,($FE) ; space key pressed. RRA ; the space bit. JR C,<A href="#L0444">L0444</a> ; back if BREAK ; else continue... <a name="L0488"></a>;; <b>MAIN-ERR</b> L0488: CALL <A href="#L06E0">L06E0</a> ; UNSTACK-Z quits if checking syntax >>> CALL <A href="#L05C2">L05C2</a> ; routine CL-EOD clears to the end of upper ; display area. LD BC,$0120 ; set line 1, column 32 for lower screen. EXX ; LD A,($4000) ; fetch the error number from ERR_NR LD BC,($4002) ; fetch the current line from PPC INC A ; test if error still $FF JR Z,<A href="#L04A8">L04A8</a> ; forward if so to MAIN-5. CP $09 ; is the error the STOP statement ? JR NZ,<A href="#L04A1">L04A1</a> ; forward if not STOP to SET-CONT to make the ; continuing line the same as current. INC BC ; else increment line number for STOP. <a name="L04A1"></a>;; <b>SET-CONT</b> L04A1: LD ($4017),BC ; store line number in OLDPPC JR NZ,<A href="#L04A8">L04A8</a> ; forward if not STOP as line number is current DEC BC ; else decrement line number again. ; Now print the report line e.g. 100/0 (terminated OK at line 100) <a name="L04A8"></a>;; <b>MAIN-5</b> L04A8: CALL <A href="#L0556">L0556</a> ; routine OUT-CODE prints line number LD A,$15 ; prepare character '/' RST 10H ; print the separator CALL <A href="#L06A1">L06A1</a> ; OUT-NUM-1 to print error-code in A. CALL <A href="#L05C2">L05C2</a> ; routine CL-EOD CALL <A href="#L013F">L013F</a> ; routine KEYBOARD JP <A href="#L0283">L0283</a> ; jump back to MAIN-EXEC ; --------------------- ; THE <b><font color=#333388>'MAIN-ADD'</font></b> BRANCH ; --------------------- ; This section allows a new BASIC line to be added to the Program. <a name="L04BA"></a>;; <b>MAIN-ADD</b> L04BA: LD ($4006),HL ; make E_PPC the new line number. EXX ; EX DE,HL ; CALL <A href="#L0747">L0747</a> ; routine CLS SBC HL,DE ; EXX ; CALL <A href="#L060A">L060A</a> ; routine LINE-ADDR PUSH HL ; JR NZ,<A href="#L04D1">L04D1</a> ; forward if line doesn't exist to MAIN-ADD1. CALL <A href="#L0624">L0624</a> ; routine NEXT-ONE gets length of old line CALL <A href="#L0666">L0666</a> ; routine RECLAIM-2 <a name="L04D1"></a>;; <b>MAIN-ADD1</b> L04D1: EXX ; INC HL ; LD B,H ; LD C,L ; LD A,L ; SUB $03 ; OR H ; CALL NZ,<A href="#L094F">L094F</a> ; routine TEST-ROOM POP HL ; JR NC,<A href="#L04F4">L04F4</a> ; double jump back to MAIN-EXEC ; not possible. PUSH BC ; DEC HL ; CALL <A href="#L05D5">L05D5</a> ; routine MAKE-ROOM INC DE ; LD HL,($400C) ; set HL from D_FILE DEC HL ; now points to end of edit line. POP BC ; restore length DEC BC ; LDDR ; copy line from edit line to prog. LD HL,($4006) ; E_PPC - line number EX DE,HL ; swap LD (HL),D ; insert high byte INC HL ; LD (HL),E ; insert low byte <a name="L04F4"></a>;; <b>MAIN-JR</b> L04F4: JP <A href="#L0283">L0283</a> ; jump back to MAIN-EXEC ; ----------------------------------------- ; THE <b><font color=#333388>'PRINT A WHOLE BASIC LINE'</font></b> SUBROUTINE ; ----------------------------------------- <a name="L04F7"></a>;; <b>OUT-LINE</b> L04F7: LD BC,($4006) ; fetch E_PPC CALL <A href="#L061C">L061C</a> ; routine CP-LINES LD D,$97 ; prepare character '>' JR Z,<A href="#L0507">L0507</a> ; forward with line cursor if line is the ; current edit line to OUT-LINE-1 LD DE,$0000 ; else replace line cursor with a ; space in D, and zero to E. RL E ; pick up any carry from CP-LINES ; should the line precede the ; current edit line. <a name="L0507"></a>;; <b>OUT-LINE-1</b> L0507: LD A,(HL) ; fetch the high byte of line number. CP $40 ; compare with end marker CALL C,<A href="#L06BF">L06BF</a> ; routine OUT-NUM-2 if a valid line number. RET NC ; return if out of screen >>> INC HL ; address the first command character. LD A,D ; fetch the space/cursor RST 10H ; print it. RET NC ; return if out of screen. <a name="L0512"></a>;; <b>OUT-LINE-2</b> L0512: SET 0,(IY+$01) ; update FLAGS - suppress a leading space <a name="L0516"></a>;; <b>OUT-LINE-3</b> L0516: LD BC,($4015) ; fetch error pointer - X_PTR AND A ; prepare to subtract. SBC HL,BC ; subtract the current address. JR NZ,<A href="#L0523">L0523</a> ; forward to OUT-LINE-4 if not an ; exact match. LD A,$B8 ; prepare inverse 'S' to show syntax error. RST 10H ; print it. RET Z ; return if at end <a name="L0523"></a>;; <b>OUT-LINE-4</b> L0523: ADD HL,BC ; restore pointer. LD A,(HL) ; fetch character. INC HL ; address next character. CP $B0 ; is character inverse 'K' ? JR Z,<A href="#L053C">L053C</a> ; forward if so to OUT-CURS. ; then cleverly split the characters into 4 streams. CP $C0 ; compare character to 192 ? JP PE,<A href="#L0559">L0559</a> ; jump forward with 64-127 to OUT-SP-CH ; thereby exiting the routine ; as it must be the 118, NEWLINE character. JR C,<A href="#L0536">L0536</a> ; forward with 0-63, 128-191 to OUT-LINE-5 ; to print simple characters and their inverse ; forms. ; that leaves tokens $C0 - $FF CALL <A href="#L0584">L0584</a> ; routine PO-TOKEN JR <A href="#L0539">L0539</a> ; forward to OUT-LINE-6 ; --- <a name="L0536"></a>;; <b>OUT-LINE-5</b> L0536: CALL <A href="#L0559">L0559</a> ; routine OUT-SP-CH <a name="L0539"></a>;; <b>OUT-LINE-6</b> L0539: RET NC ; return if out of screen. >> JR <A href="#L0516">L0516</a> ; else back to OUT-LINE-3 for more. ; --------------------------------------------------------------------------- ; Z80 PARITY/OVERFLOW FLAG: ; ------------------------ ; The use of this flag is two-fold depending on the type of operation. ; It indicates the parity of the result of a LOGICAL operation such as an AND, ; OR, XOR by being set PE if there are an even number of set bits and reset ; PO if there are an odd number of set bits. ; so 10101010 is parity even, 00000001 is parity odd. ; JP PE, LABEL ; JP PO, LABEL are obvious. ; For MATHEMATICAL operations, (ADD, SUB, CP etc.) the P/V bit indicates a ; carry out of bit position 6 of the accumulator if signed values are being ; used. ; This indicates an overflow of a result greater than 127, which carries ; into bit 7, the sign bit. ; So as CP is just a SUB with the result thrown away. ; $C0 SUB $CO gives result $00 (PO - no overflow from 6 to 7) ; $8O SUB $C0 gives result $C0 (PO - no overflow from 6 to 7) ; $00 SUB $C0 gives result $40 (PO - no overflow from 6 to 7) ; $40 SUB $CO gives result $80 (PE - overflow from 6 to 7) ; The overflow flag is similarly set following 16-bit addition and subtraction ; routines. ; --------------------------------------------------------------------------- ; ----------------------------- ; THE <b><font color=#333388>'PRINT THE CURSOR'</font></b> BRANCH ; ----------------------------- <a name="L053C"></a>;; <b>OUT-CURS</b> L053C: BIT 2,(IY+$01) ; test FLAGS - K-mode ? JR NZ,<A href="#L0543">L0543</a> ; skip to OUT-K if 'K' mode. INC A ; change from 'K' to 'L' cursor. <a name="L0543"></a>;; <b>OUT-K</b> L0543: RST 10H ; print the cursor. JR <A href="#L0539">L0539</a> ; back to OUT-LINE-6 above. ; ----------------------------------------------------- ; THE <b><font color=#333388>'PRINTING CHARACTERS IN A BASIC LINE'</font></b> SUBROUTINES ; ----------------------------------------------------- <a name="L0546"></a>;; <b>OUT-SP-2</b> L0546: LD A,E ; transfer E to A ; register E will be ; $FF - no leading space. ; $01 - the leading space itself. ; $1C - '0' from a previous non-space print. RLCA ; test for the RRCA ; value $FF. RET C ; return if no leading space JR <A href="#L055C">L055C</a> ; forward to OUT-LD-SP ; --- ; --> The Entry Point. <a name="L054C"></a>;; <b>OUT-SP-NO</b> L054C: XOR A ; set accumulator to zero. <a name="L054D"></a>;; <b>OUT-SP-1</b> L054D: ADD HL,BC ; addition of negative number. INC A ; increment the digit. JR C,<A href="#L054D">L054D</a> ; back while overflow exists to OUT-SP-1 SBC HL,BC ; else reverse the last addition. DEC A ; and decrement the digit. JR Z,<A href="#L0546">L0546</a> ; back to OUT-SP-2 if digit is zero again. ; else continue to print the final digit using OUT-CODE. <a name="L0556"></a>;; <b>OUT-CODE</b> L0556: LD E,$1C ; load E with '0' ; <font color=#9900FF>Note.</font> that E will remain as such for all ; further calls. The leading space is no more. ADD A,E ; add the digit 1-9 to give '1' to '9' <a name="L0559"></a>;; <b>OUT-SP-CH</b> L0559: AND A ; test value for space. JR Z,<A href="#L0560">L0560</a> ; skip if zero to PRINT-A-2 <a name="L055C"></a>;; <b>OUT-LD-SP</b> L055C: RES 0,(IY+$01) ; signal allow leading space to FLAGS ; and continue... ; ------------------------------ ; THE <b><font color=#333388>'MAIN PRINTING'</font></b> SUBROUTINE ; ------------------------------ ; This is a continuation of the PRINT restart. ; It is used primarily to print to the dynamic screen checking free memory ; before every character is printed. ; However it can also be used as an invisible process to 'sprint' the line ; number of a BASIC line to the Edit Line by ED-EDIT setting DE from E_LINE. ; ; As lines are unexpanded, then when the column count is reduced from 32 to 0 a ; newline is inserted before the character and the column count is reset. <a name="L0560"></a>;; <b>PRINT-A-2</b> L0560: EXX ; switch sets. LD H,A ; preserve character in H. ; <font color=#9900FF>Note.</font> this is restored by TEST-RM-2 RLA ; rotate character twice to RLA ; test bit 6 - sets carry for NEWLINE. DEC C ; decrease column count - affects zero / sign. JR NC,<A href="#L0569">L0569</a> ; forward if 0-63 or inverse to NO-NL ; else the incoming character is a NEWLINE $76 LD C,$00 ; set column to zero without disturbing flags. ; if this is a received NEWLINE. ; this will be set to 32 if a subsequent ; character is printed <a name="L0569"></a>;; <b>NO-NL</b> L0569: JP M,<A href="#L0574">L0574</a> ; jump to PR-SPR if column was originally 0 JR C,<A href="#L057C">L057C</a> ; forward to PRI-CHAR with a received NEWLINE. JR NZ,<A href="#L057C">L057C</a> ; forward if column not yet reduced to zero ; to PRI-CHAR ; else an automatic newline is required before the received character as ; we are at end of line. LD A,$76 ; prepare the newline LD (DE),A ; insert at screen position INC DE ; increase the address pointer. <a name="L0574"></a>;; <b>PR-SPR</b> L0574: JR C,<A href="#L0578">L0578</a> ; skip if a received newline to PRI-SKIP LD C,$20 ; reset column to 32 decimal. <a name="L0578"></a>;; <b>PRI-SKIP</b> L0578: AND A ; clear carry now to signal failure should the ; next test fail. DEC B ; decrease line. JR Z,<A href="#L0582">L0582</a> ; forward with out of screen to PR-END. <a name="L057C"></a>;; <b>PRI-CH</b> L057C: LD L,B ; transfer line number, B to L for next routine. CALL <A href="#L0958">L0958</a> ; routine TEST-RM-2 tests room. ; (character is in H returned in A) ; carry set if there is room. LD (DE),A ; insert chr at screen (or edit line). INC DE ; increase destination address. <a name="L0582"></a>;; <b>PR-END</b> L0582: EXX ; switch to protect registers. RET ; return ; ------------------------------- ; THE <b><font color=#333388>'TOKEN PRINTING'</font></b> SUBROUTINE ; ------------------------------- <a name="L0584"></a>;; <b>PO-TOKEN</b> L0584: CALL <A href="#L05A8">L05A8</a> ; routine PO-SEARCH locates token JR NC,<A href="#L0592">L0592</a> ; forward to PO-LOOP if first character is ; not alphanumeric. e.g. '**' ; else consider a leading space. BIT 0,(IY+$01) ; test FLAGS - leading space allowed ? JR NZ,<A href="#L0592">L0592</a> ; forward to PO-LOOP if not. ; else print a leading space. XOR A ; prepare a space RST 10H ; print it RET NC ; return if out of screen. ; now enter a loop to print each character and then consider a trailing space. <a name="L070A"></a>;; <b>PO-LOOP</b> L0592: LD A,(BC) ; fetch character from token table. AND $3F ; mask to give range ' ' to 'Z' CALL <A href="#L0559">L0559</a> ; routine OUT-SP-CH RET NC ; return if out of screen. LD A,(BC) ; reload the character INC BC ; point to next. ADD A,A ; test for the inverted bit. JR NC,<A href="#L0592">L0592</a> ; loop back if not inverted to PO-LOOP ; CP $38 ; compare with what was '0' before doubling. RET C ; return if less. i.e. not a command. >> XOR A ; else prepare a space SET 0,(IY+$01) ; update FLAGS - use no leading space JR <A href="#L0560">L0560</a> ; back to PRINT-A-2 for trailing space. >> ; ----------------------------- ; THE <b><font color=#333388>'TABLE SEARCH'</font></b> SUBROUTINE ; ----------------------------- <a name="L05A8"></a>;; <b>PO-SEARCH</b> L05A8: PUSH HL ; * preserve character pointer LD HL,$00BA ; point to start of the table SUB (HL) ; test against the threshold character 212 INC HL ; address next in table. ('?' + $80 ) JR C,<A href="#L05B9">L05B9</a> ; forward to PO-FOUND if less than 212 ; to print a question mark. INC A ; make range start at 1 for chr 212. ; note - should the required token be 212 ; the printable quote character then the ; pointer currently addresses '"' + $80. LD B,A ; save reduced token in B as a counter. <a name="L05B2"></a>;; <b>PO-STEP</b> L05B2: BIT 7,(HL) ; test for inverted bit INC HL ; increase address JR Z,<A href="#L05B2">L05B2</a> ; back to PO-STEP for inverted bit DJNZ <A href="#L05B2">L05B2</a> ; decrement counter and loop back to PO-STEP ; until at required token. <a name="L05B9"></a>;; <b>PO-FOUND</b> L05B9: LD B,H ; transfer the address LD C,L ; to BC. POP HL ; * restore string address LD A,(BC) ; fetch first character from token. AND $3F ; mask off range 0-63d, SPACE to Z ADD A,$E4 ; add value 228 RET ; return with carry set if alphanumeric and a ; leading space is required. ; ------------------------------------- ; THE <b><font color=#333388>'CLEAR TO END OF DISPLAY'</font></b> ROUTINE ; ------------------------------------- <a name="L05C2"></a>;; <b>CL-EOD</b> L05C2: EXX ; switch in the set with screen values. XOR A ; clear accumulator. CP B ; compare with line counter - 0 to 23. JR Z,<A href="#L05D0">L05D0</a> ; forward if clear to SET-EOD. CP C ; compare to column count - 0 to 32. LD A,$76 ; prepare a NEWLINE. JR Z,<A href="#L05CE">L05CE</a> ; forward, if zero, to CL-EOL. <a name="L05CC"></a>;; <b>INS-CR</b> L05CC: LD (DE),A ; insert a newline/carriage return. INC DE ; address next position. <a name="L05CE"></a>;; <b>CL-EOL</b> L05CE: DJNZ <A href="#L05CC">L05CC</a> ; reduce line counter and loop back to INS-CR. <a name="L05D0"></a>;; <b>SET-EOD</b> L05D0: LD ($4010),DE ; update DF_END - display file end. RET ; return. ; -------------------------- ; THE <b><font color=#333388>'MAKE-ROOM'</font></b> SUBROUTINE ; -------------------------- <a name="L05D5"></a>;; <b>MAKE-ROOM</b> L05D5: CALL <A href="#L05DF">L05DF</a> ; routine POINTERS also sets BC LD HL,($4010) ; fetch new display file end DF_END EX DE,HL ; switch source/destination. LDDR ; now make the room. RET ; return. ; with HL pointing at first new location. ; ------------------------- ; THE <b><font color=#333388>'POINTERS'</font></b> SUBROUTINE ; ------------------------- <a name="L05DF"></a>;; <b>POINTERS</b> L05DF: PUSH AF ; PUSH HL ; LD HL,$4008 ; VARS LD A,$05 ; <a name="L05E6"></a>;; <b>PTR-NEXT</b> L05E6: LD E,(HL) ; INC HL ; LD D,(HL) ; EX (SP),HL ; AND A ; SBC HL,DE ; ADD HL,DE ; EX (SP),HL ; JR NC,<A href="#L05FA">L05FA</a> ; forward to PTR-DONE PUSH DE ; EX DE,HL ; ADD HL,BC ; EX DE,HL ; LD (HL),D ; DEC HL ; LD (HL),E ; INC HL ; POP DE ; <a name="L05FA"></a>;; <b>PTR-DONE</b> L05FA: INC HL ; DEC A ; JR NZ,<A href="#L05E6">L05E6</a> ; back to PTR-NEXT for all five ; dynamic variables. ; now find the size of the block to be moved. EX DE,HL ; POP DE ; POP AF ; AND A ; SBC HL,DE ; LD B,H ; LD C,L ; INC BC ; ADD HL,DE ; EX DE,HL ; RET ; return -> ; -------------------------- ; THE <b><font color=#333388>'LINE-ADDR'</font></b> SUBROUTINE ; -------------------------- <a name="L060A"></a>;; <b>LINE-ADDR</b> L060A: PUSH HL ; save the given line number. LD HL,$4028 ; start of PROG LD D,H ; transfer the address LD E,L ; to the DE register pair. <a name="L0610"></a>;; <b>LINE-AD-1</b> L0610: POP BC ; the given line number. EX DE,HL ; CALL <A href="#L061C">L061C</a> ; routine CP-LINES RET NC ; return if carry set >> PUSH BC ; otherwise save given line number CALL <A href="#L0624">L0624</a> ; routine NEXT-ONE JR <A href="#L0610">L0610</a> ; back to LINE-AD-1 to consider the next ; line of the program. ; ------------------------------------- ; THE <b><font color=#333388>'COMPARE LINE NUMBERS'</font></b> SUBROUTINE ; ------------------------------------- <a name="L061C"></a>;; <b>CP-LINES</b> L061C: LD A,(HL) ; fetch the high byte of the addressed line CP B ; number and compare it. RET NZ ; return if they do not match. INC HL ; next compare the low bytes. LD A,(HL) ; DEC HL ; CP C ; RET ; return with carry flag set if the addressed ; line number has yet to reach the ; given line number. ;------------------------------------------------------------------------ ; Storage of variables. For full details - see Page 107 ; ZX80 BASIC Programming by Hugo Davenport 1980. ; It is bits 7-5 of the first character of a variable that allow ; the five types to be distinguished. Bits 4-0 are the reduced letter. ; So any variable name is higher that $3F and can be distinguished ; also from the variables area end-marker $80. ; ; 76543210 meaning brief outline of format after letter. ; -------- ------------------------ ----------------------- ; 011 simple integer variable. 2 bytes. (after letter) ; 010 long-named integer variable 2 bytes. (after inverted name) ; 100 string letter + contents + $01. ; 101 array of integers letter + max subs byte + subs * 2. ; 111 for-next loop variable. 7 bytes - letter, value, limit, line. ; 10000000 the variables end-marker. ; ; <font color=#9900FF>Note.</font> any of the above six will serve as a program end-marker. ; ; ----------------------------------------------------------------------- ; ------------------------- ; THE <b><font color=#333388>'NEXT-ONE'</font></b> SUBROUTINE ; ------------------------- <a name="L0624"></a>;; <b>NEXT-ONE</b> L0624: PUSH HL ; save address of current line or variable. LD A,(HL) ; fetch the first byte. ADD A,A ; test bits 7 and 6 JP M,<A href="#L0635">L0635</a> ; jump forward if simple, long-named or for-next ; control variable to NO-SLNFM JR C,<A href="#L0643">L0643</a> ; forward if string or arrays to NO-STR-AR ; that leaves program line numbers. INC HL ; step past high byte LD A,$76 ; the search is for newline <a name="L062F"></a>;; <b>NO-SEARCH</b> L062F: INC HL ; skip to next address past low byte. LD B,A ; save search byte in B to create ; a large value in BC so that search is ; not curtailed. CPIR ; and locate the known character. JR <A href="#L0652">L0652</a> ; forward to ??? with HL addressing ; the following character. ; --- ; the branch was here with simple, long-named and for-next variables <a name="L0635"></a>;; <b>NO-SLNFN</b> L0635: LD BC,$0002 ; presume a for-next variable (1+2 cells) JR C,<A href="#L063B">L063B</a> ; skip forward if for-next variable. LD C,B ; set C to zero - just one cell for simple ; and long-named. <a name="L063B"></a>;; <b>NO-FNXT</b> L063B: RLA ; original bit 5 is now bit 7. <a name="L063C"></a>;; <b>NO-LNLP</b> L063C: RLA ; test original bit 5 of letter. INC HL ; advance address. LD A,(HL) ; pick up next byte - possibly a letter JR NC,<A href="#L063C">L063C</a> ; back if originally long-named or if ; on subsequent loops character is not inverted ; whatever the route we are now pointing at the first cell with the number ; of cells less one in register C. JR <A href="#L064F">L064F</a> ; forward to NO-CELLS to calculate space to the ; end of variable. ; --- ; the branch was here with either single strings or numeric array variables <a name="L0643"></a>;; <b>NO-STR_AR</b> L0643: AND $40 ; test shifted bit 6 - will be set for arrays LD A,$01 ; set search for null terminator JR Z,<A href="#L062F">L062F</a> ; back if not an array to NO-SEARCH to ; search for the end of string. ; the object is a NUMERIC ARRAY INC HL ; point to maximum subscription LD A,(HL) ; and fetch INC HL ; point to first cell. LD B,$00 ; prepare to index LD C,A ; max subscription to C ; and continue to find following byte. <a name="L064F"></a>;; <b>NXT-O-6</b> L064F: INC BC ; bump the range ADD HL,BC ; add to start ADD HL,BC ; add again as each cell is two bytes. <a name="L0652"></a>;; <b>NXT-O-7</b> L0652: POP DE ; restore previous address to DE and ; continue into the difference routine... ; --------------------------- ; THE <b><font color=#333388>'DIFFERENCE'</font></b> SUBROUTINE ; --------------------------- <a name="L0653"></a>;; <b>DIFFER</b> L0653: AND A ; prepare to subtract. SBC HL,DE ; calculate the length of the line/var LD B,H ; transfer the length LD C,L ; to the BC register pair. ADD HL,DE ; reform the address of next one in HL. EX DE,HL ; swap pointers RET ; return. ; ------------------------------ ; THE <b><font color=#333388>'CLEAR'</font></b> COMMAND SUBROUTINE ; ------------------------------ ; The CLEAR command removes all BASIC variables. <a name="L065B"></a>;; <b>CLEAR</b> L065B: LD HL,($400A) ; set HL to E_LINE. DEC HL ; decrement to point to the $80 end-marker. LD DE,($4008) ; set start from VARS system variable. ; ---------------------------- ; THE <b><font color=#333388>'RECLAIMING'</font></b> SUBROUTINES ; ---------------------------- <a name="L0663"></a>;; <b>RECLAIM-1</b> L0663: CALL <A href="#L0653">L0653</a> ; routine DIFFER <a name="L0666"></a>;; <b>RECLAIM-2</b> L0666: PUSH BC ; LD A,B ; CPL ; LD B,A ; LD A,C ; CPL ; LD C,A ; INC BC ; CALL <A href="#L05DF">L05DF</a> ; routine POINTERS EX DE,HL ; POP HL ; ADD HL,DE ; PUSH DE ; LDIR ; POP HL ; RET ; return. ; ---------------------------------------- ; THE <b><font color=#333388>'INTEGER TO ALTERNATE HL'</font></b> SUBROUTINE ; ---------------------------------------- <a name="L0679"></a>;; <b>INT-TO-HL</b> L0679: LD A,(HL) ; fetch first digit EXX ; switch LD HL,$0000 ; initialize result register to zero. LD B,H ; make B zero also. <a name="L067F"></a>;; <b>DEC-LP</b> L067F: SUB $1C ; subtract chr '0' JR C,<A href="#L069A">L069A</a> ; forward to STOR-RSLT if less. >> CP $0A ; compare with 'ten' JR NC,<A href="#L069A">L069A</a> ; forward to STOR-RSLT if higher than '9'. >> LD C,A ; save unit in C. ; now test that the result is not about to enter the 32768 - 65535 region. LD A,$0D ; value 13 to A CP H ; compare to result_hi JR NC,<A href="#L068E">L068E</a> ; forward if less to NO-OVERFLW LD H,A ; else maintain the overflow condition. <a name="L068E"></a>;; <b>NO-OVRFLW</b> L068E: LD D,H ; copy HL. LD E,L ; to DE. ADD HL,HL ; double result ADD HL,HL ; and again. ADD HL,DE ; now * 5 ADD HL,HL ; now *10 ADD HL,BC ; add in new digit. EXX ; switch RST 18H ; NXT-CH-SP EXX ; switch JR <A href="#L067F">L067F</a> ; loop back to DEC-LP for more digits. ; ------------------------------------- ; THE <b><font color=#333388>'STORE INTEGER RESULT'</font></b> SUBROUTINE ; ------------------------------------- <a name="L069A"></a>;; <b>STOR-RSLT</b> L069A: LD A,H ; transfer high byte to A. LD ($4022),HL ; set value of expression RESULT EXX ; switch RLA ; sets carry if higher than 32767 RET ; return. ; ------------------------------------------------ ; THE <b><font color=#333388>'REPORT AND LINE NUMBER PRINTING'</font></b> SUBROUTINE ; ------------------------------------------------ ; Actually the first entry point prints any number in the ; range -32768 to 32767. ; --> This entry point prints a number in BC. <a name="L06A1"></a>;; <b>OUT-NUM-1</b> L06A1: PUSH DE ; preserve registers PUSH HL ; throughout LD H,B ; transfer number LD L,C ; to be printed to HL. BIT 7,B ; test the sign bit JR Z,<A href="#L06B5">L06B5</a> ; forward if positive to OUT-NUM-P LD A,$12 ; prepare character '-' CALL <A href="#L0559">L0559</a> ; routine OUT-SP-CH JR NC,<A href="#L06DD">L06DD</a> ; forward if out of screen to OUT-NUM-4 LD HL,$0001 ; else make the negative number SBC HL,BC ; positive. ; at this stage the number is positive <a name="L06B5"></a>;; <b>OUT-NUM-P</b> L06B5: LD E,$FF ; signal no leading space. LD BC,$D8F0 ; prepare the value -10000 CALL <A href="#L054C">L054C</a> ; routine OUT-SP-NO will print the first digit ; of a 5-digit number but nothing if smaller. JR <A href="#L06C8">L06C8</a> ; forward to OUT-NUM-3 ; to consider other four digits in turn. ; (with carry set from a successful print) ; --- ; --> This entry point prints a BASIC line number addressed by HL. <a name="L06BF"></a>;; <b>OUT-NUM-2</b> L06BF: PUSH DE ; save DE throughout LD D,(HL) ; fetch high byte of number to D INC HL LD E,(HL) ; fetch low byte of number to E PUSH HL ; save HL now till the end. EX DE,HL ; number to HL. LD E,$00 ; prepare a leading space SCF ; set carry flag for subtractions. ; both paths converge here. <a name="L06C8"></a>;; <b>OUT-NUM-3</b> L06C8: LD BC,$FC18 ; the value -1000 CALL C,<A href="#L054C">L054C</a> ; routine OUT-SP-NO LD BC,$FF9C ; the value -100 CALL C,<A href="#L054C">L054C</a> ; routine OUT-SP-NO LD C,$F6 ; the value -10 CALL C,<A href="#L054C">L054C</a> ; routine OUT-SP-NO LD A,L ; the remainder. CALL C,<A href="#L0556">L0556</a> ; routine OUT-CODE <a name="L06DD"></a>;; <b>OUT-NUM-4</b> L06DD: POP HL ; restore original POP DE ; registers. RET ; return. ; -------------------------- ; THE <b><font color=#333388>'UNSTACK-Z'</font></b> SUBROUTINE ; -------------------------- <a name="L06E0"></a>;; <b>UNSTACK-Z</b> L06E0: BIT 7,(IY+$01) ; test FLAGS - Checking Syntax ? POP HL ; drop the return address RET Z ; return if so. ; else fetch screen coordinates alternate registers for the run-time situation. EXX LD DE,($400E) ; fetch display print position DF_EA LD BC,($4024) ; fetch line and column from SPOSN EXX ; exchange and continue... ; and jump back to the calling routine... ; ------------------ ; THE <b><font color=#333388>'USR'</font></b> FUNCTION ; ------------------ <a name="L06F0"></a>;; <b>USR</b> L06F0: JP (HL) ; that appears to be it. ; --------------------------- ; THE <b><font color=#333388>'PRINT ITEM'</font></b> SUBROUTINE ; --------------------------- <a name="L06F1"></a>;; <b>PR-ITEM</b> L06F1: BIT 7,(IY+$00) ; ERR_NR RET Z ; return if an error has already been ; encountered. CALL <A href="#L06E0">L06E0</a> ; UNSTACK-Z quits if checking syntax LD HL,($4022) ; fetch result of SCANNING from RESULT BIT 6,(IY+$01) ; test FLAGS for result type. JR Z,<A href="#L070C">L070C</a> ; forward to PR-STRING if type string. LD B,H ; transfer result LD C,L ; to BC register pair. CALL <A href="#L06A1">L06A1</a> ; routine OUT-NUM-1 JR <A href="#L0723">L0723</a> ; forward to PO-CHECK to check for ; success and store position ; ----------------------------- ; THE <b><font color=#333388>'PRINT STRING'</font></b> SUBROUTINE ; ----------------------------- <a name="L0709"></a>;; <b>PO-CHAR</b> L0709: RST 10H ; PRINT-A <a name="L070A"></a>;; <b>PO-LOOP</b> L070A: JR NC,<A href="#L0725">L0725</a> ; forward to ERROR-05 with carry ; Out of screen. ; --> Entry Point. <a name="L070C"></a>;; <b>PR-STRING</b> L070C: LD A,(HL) ; fetch a character. INC HL ; increment pointer. CP $01 ; is it null-terminator. JR Z,<A href="#L073A">L073A</a> ; forward to PO-STORE if so. BIT 6,A ; test if simple character or inverse JR Z,<A href="#L0709">L0709</a> ; back to PO-CHAR if so CALL <A href="#L0584">L0584</a> ; routine PO-TOKEN to print ; ranges $40 - $7f, $0C - $FF JR <A href="#L070A">L070A</a> ; loop back to PO-LOOP ; -------------------------------- ; THE <b><font color=#333388>'CARRIAGE RETURN'</font></b> SUBROUTINE ; -------------------------------- <a name="L071B"></a>;; <b>PRINT-CR</b> L071B: CALL <A href="#L06E0">L06E0</a> ; UNSTACK-Z quits if checking syntax LD A,$76 ; prepare a NEWLINE character CALL <A href="#L0559">L0559</a> ; routine OUT-SP-CH prints it ; returning with carry reset if there ; was no room on the screen. <a name="L0723"></a>;; <b>PO-CHECK</b> L0723: JR C,<A href="#L073A">L073A</a> ; forward to PO-STORE if OK <a name="L0725"></a>;; <b>ERROR-05</b> L0725: RST 08H ; ERROR restart DEFB $04 ; No more room on screen. ; ------------------------ ; THE <b><font color=#333388>'PO-FILL'</font></b> SUBROUTINE ; ------------------------ <a name="L0727"></a>;; <b>PO-FILL</b> L0727: CALL <A href="#L06E0">L06E0</a> ; UNSTACK-Z return if checking syntax. SET 0,(IY+$01) ; signal no leading space. <a name="L072E"></a>;; <b>PO-SPACE</b> L072E: XOR A ; prepare a space RST 10H ; PRINT-A outputs the character. JR NC,<A href="#L0725">L0725</a> ; back to ERROR-05 if out of screen EXX ; LD A,C ; get updated column EXX ; DEC A ; decrement it. AND $07 ; isolate values 0 - 7 JR NZ,<A href="#L072E">L072E</a> ; back to PO-SPACE for more. ; ------------------------------- ; THE <b><font color=#333388>'POSITION STORE'</font></b> SUBROUTINE ; ------------------------------- <a name="L073A"></a>;; <b>PO-STORE</b> L073A: EXX ; switch in the set that maintains the print ; positions in the registers. EX DE,HL ; switch print position to HL for easier coding. <a name="L073C"></a>;; <b>PO-STOR-2</b> L073C: LD ($4024),BC ; set SPOSN to line/column LD ($400E),HL ; set DF_EA to output address LD ($4010),HL ; set DF_END output address RET ; return. ; ---------------------------- ; THE <b><font color=#333388>'CLS'</font></b> COMMAND SUBROUTINE ; ---------------------------- <a name="L0747"></a>;; <b>CLS</b> L0747: LD HL,($400C) ; fetch start of display from D_FILE LD (HL),$76 ; insert a single newline. INC HL ; advance address. LD BC,$1721 ; set line to 23 and column to 33. JR <A href="#L073C">L073C</a> ; back to PO-STOR-2 above ; ------------------- ; THE <b><font color=#333388>'SYNTAX TABLES'</font></b> ; ------------------- <a name="L0752"></a>;; <b>i.</b> The offset table L0752: DEFB <A href="#L07A1">L07A1</a> - $ ; $4F offset to $07A1 P-LIST DEFB <A href="#L077F">L077F</a> - $ ; $2C offset to $077F P-RETURN DEFB <A href="#L07B8">L07B8</a> - $ ; $64 offset to $07B8 P-CLS DEFB <A href="#L0794">L0794</a> - $ ; $3F offset to $0794 P-DIM DEFB <A href="#L07AF">L07AF</a> - $ ; $59 offset to $07AF P-SAVE DEFB <A href="#L0782">L0782</a> - $ ; $2B offset to $0782 P-FOR DEFB <A href="#L076F">L076F</a> - $ ; $17 offset to $076F P-GO-TO DEFB <A href="#L07A4">L07A4</a> - $ ; $4B offset to $07A4 P-POKE DEFB <A href="#L0790">L0790</a> - $ ; $36 offset to $0790 P-INPUT DEFB <A href="#L07A9">L07A9</a> - $ ; $4E offset to $07A9 P-RANDOMISE DEFB <A href="#L076C">L076C</a> - $ ; $10 offset to $076C P-LET DEFB <A href="#L07BB">L07BB</a> - $ ; $5E offset to $07BB P-CH-END DEFB <A href="#L07BB">L07BB</a> - $ ; $5D offset to $07BB P-CH-END DEFB <A href="#L0789">L0789</a> - $ ; $2A offset to $0789 P-NEXT DEFB <A href="#L078D">L078D</a> - $ ; $2D offset to $078D P-PRINT DEFB <A href="#L07BB">L07BB</a> - $ ; $5A offset to $07BB P-CH-END DEFB <A href="#L07C2">L07C2</a> + 1 - $ ; $61 offset to $07C3 P-NEW DEFB <A href="#L079E">L079E</a> - $ ; $3B offset to $079E P-RUN DEFB <A href="#L077C">L077C</a> - $ ; $18 offset to $077C P-STOP DEFB <A href="#L07B2">L07B2</a> - $ ; $4D offset to $07B2 P-CONTINUE DEFB <A href="#L0773">L0773</a> - $ ; $0D offset to $0773 P-IF DEFB <A href="#L0778">L0778</a> - $ ; $11 offset to $0778 P-GOSUB DEFB <A href="#L07AC">L07AC</a> - $ ; $44 offset to $07AC P-LOAD DEFB <A href="#L07B5">L07B5</a> - $ ; $4C offset to $07B5 P-CLEAR DEFB <A href="#L079B">L079B</a> - $ ; $31 offset to $079B P-REM DEFB <A href="#L07BB">L07BB</a> - $ ; $50 offset to $07BB P-CH-END <a name="L076C"></a>;; <b>ii.</b> The parameter table. <a name="L076C"></a>;; <b>P-LET</b> L076C: DEFB $01 ; Class-01 - a variable is required. DEFB $E3 ; separator '=' DEFB $02 ; Class-02 - an expression, of type integer or ; string must follow. <a name="L076F"></a>;; <b>P-GO-TO</b> L076F: DEFB $06 ; Class-06 - a numeric expression must follow. DEFB $00 ; Class-00 - no further operands. DEFW <A href="#L0934">L0934</a> ; address: $0934 <a name="L0773"></a>;; <b>P-IF</b> L0773: DEFB $06 ; Class-06 - a numeric expression must follow. DEFB $D5 ; separator 'THEN' DEFB $05 ; Class-05 - variable syntax checked entirely ; by routine. DEFW <A href="#L08B9">L08B9</a> ; address: $08B9 <a name="L0778"></a>;; <b>P-GOSUB</b> L0778: DEFB $06 ; Class-06 - a numeric expression must follow. DEFB $00 ; Class-00 - no further operands. DEFW <A href="#L0943">L0943</a> ; address: $0943 <a name="L077C"></a>;; <b>P-STOP</b> L077C: DEFB $00 ; Class-00 - no further operands. DEFW <A href="#L092E">L092E</a> ; address: $092E <a name="L077F"></a>;; <b>P-RETURN</b> L077F: DEFB $00 ; Class-00 - no further operands. DEFW <A href="#L0965">L0965</a> ; address: $0965 <a name="L0782"></a>;; <b>P-FOR</b> L0782: DEFB $04 ; Class-04 - a single-character variable must ; follow. DEFB $E3 ; separator '=' DEFB $06 ; Class-06 - a numeric expression must follow. DEFB $D6 ; separator 'TO' DEFB $05 ; Class-05 - variable syntax checked entirely ; by routine. DEFW <A href="#L08C4">L08C4</a> ; address: $08C4 <a name="L0789"></a>;; <b>P-NEXT</b> L0789: DEFB $04 ; Class-04 - a single-character variable must ; follow. DEFB $00 ; Class-00 - no further operands. DEFW <A href="#L08F9">L08F9</a> ; address: $08F9 <a name="L078D"></a>;; <b>P-PRINT</b> L078D: DEFB $05 ; Class-05 - variable syntax checked entirely ; by routine. DEFW <A href="#L0972">L0972</a> ; address: $0972 <a name="L0790"></a>;; <b>P-INPUT</b> L0790: DEFB $01 ; Class-01 - a variable is required. DEFB $00 ; Class-00 - no further operands. DEFW <A href="#L099A">L099A</a> ; address: $099A <a name="L0794"></a>;; <b>P-DIM</b> L0794: DEFB $04 ; Class-04 - a single-character variable must ; follow. DEFB $DA ; separator '(' DEFB $06 ; Class-06 - a numeric expression must follow. DEFB $D9 ; separator ')' DEFB $00 ; Class-00 - no further operands. DEFW <A href="#L0CD3">L0CD3</a> ; address: $0CD3 <a name="L079B"></a>;; <b>P-REM</b> L079B: DEFB $05 ; Class-05 - variable syntax checked entirely ; by routine. DEFW <A href="#L084A">L084A</a> ; address: $084A <a name="L079E"></a>;; <b>P-RUN</b> L079E: DEFB $03 ; Class-03 - a numeric expression may follow ; otherwise zero will be used. DEFW <A href="#L093D">L093D</a> ; address: $093D <a name="L07A1"></a>;; <b>P-LIST</b> L07A1: DEFB $03 ; Class-03 - a numeric expression may follow ; else default to zero. DEFW <A href="#L0256">L0256</a> ; Address: $0256 <a name="L07A4"></a>;; <b>P-POKE</b> L07A4: DEFB $06 ; Class-06 - a numeric expression must follow. DEFB $D8 ; separator ',' DEFB $05 ; Class-05 - variable syntax checked entirely ; by routine. DEFW <A href="#L09D1">L09D1</a> ; address: $09D1 <a name="L07A9"></a>;; <b>P-RANDOMISE</b> L07A9: DEFB $03 ; Class-03 - a numeric expression may follow ; otherwise zero will be used. DEFW <A href="#L0923">L0923</a> ; address: $0923 <a name="L07AC"></a>;; <b>P-LOAD</b> L07AC: DEFB $00 ; Class-00 - no further operands. DEFW <A href="#L0206">L0206</a> ; address: $0206 <a name="L07AF"></a>;; <b>P-SAVE</b> L07AF: DEFB $00 ; Class-00 - no further operands. DEFW <A href="#L01B6">L01B6</a> ; address: $01B6 <a name="L07B2"></a>;; <b>P-CONTINUE</b> L07B2: DEFB $00 ; Class-00 - no further operands. DEFW <A href="#L0930">L0930</a> ; address: $0930 <a name="L07B5"></a>;; <b>P-CLEAR</b> L07B5: DEFB $00 ; Class-00 - no further operands. DEFW <A href="#L065B">L065B</a> ; address: $065B <a name="L07B8"></a>;; <b>P-CLS</b> L07B8: DEFB $00 ; Class-00 - no further operands. DEFW <A href="#L0747">L0747</a> ; Address: $0747 <a name="L07BB"></a>;; <b>P-CH-END</b> L07BB: DEFB $05 ; Class-05 - variable syntax checked entirely ; by routine. DEFW <A href="#L0844">L0844</a> ; address: $0844 ; <font color=#9900FF>Note.</font> one would expect the entry for the P-NEW parameters to be here. ; It should consist of a class 0, followed by the address word zero as, ; without any protected RAM, the NEW command is no more sophisticated than ; a reset. ; However, there just isn't room. All 4096 bytes of the ROM have been ; put to good use so the required entry, three zero bytes, is embedded ; in the next routine, adding a harmless NOP to make up the three zero bytes. ; Aye, and you try telling young people of today that. And they won't ; believe you. ; ------------------------------ <a name="L07BE"></a>;; <b>MAIN-G</b> L07BE: DEC HL LD ($4026),HL ; CH_ADD <a name="L07C2"></a>;; <b>P-NEW-1</b> L07C2: LD HL,$0000 ; prepare to clear error pointer. NOP ; <font color=#9900FF>Note.</font> See comment above. LD ($4015),HL ; clear X_PTR LD HL,$4019 ; address FLAGX BIT 5,(HL) ; is INPUT mode set ? JR Z,<A href="#L07D7">L07D7</a> ; forward if not to E-LINE-NO ; else runtime input. RES 7,(HL) ; signal L mode. LD B,(HL) ; FLAGX to B for class routine. RST 18H ; NXT-CH-SP advances. JP <A href="#L0889">L0889</a> ; jump forward to VAL-FETCH. ; ----------------------- ; THE <b><font color=#333388>'E-LINE-NO'</font></b> SECTION ; ----------------------- <a name="L07D7"></a>;; <b>E-LINE-NO</b> L07D7: SET 7,(HL) ; update FLAGX - signal K mode RST 20H ; NEXT-CHAR CALL <A href="#L0679">L0679</a> ; routine INT-TO-HL puts the BASIC Line Number ; into HL' JR C,<A href="#L07E5">L07E5</a> ; forward if a negative to insert error. ; else test against upper limit. EXX ; LD DE,$D8F0 ; value -9999 ADD HL,DE ; EXX ; <a name="L07E5"></a>;; <b>E-L-ERR</b> L07E5: CALL C,<A href="#L08AE">L08AE</a> ; routine INS-ERR if greater than 9999 ; ----------------------- ; THE <b><font color=#333388>'LINE-SCAN'</font></b> SECTION ; ----------------------- <a name="L07E8"></a>;; <b>LINE-SCAN</b> L07E8: CALL <A href="#L001A">L001A</a> ; get the COMMAND CHARACTER. RES 7,(IY+$19) ; update FLAGX signal not K mode anymore. LD BC,$0000 ; this also sets B to zero for later. LD ($4022),BC ; default RESULT to ZERO ; for, say, RUN without an operand. CP $76 ; compare to just newline RET Z ; return if so. ; for example with a space for formatting. LD C,A ; transfer the character to C RST 20H ; NEXT_CHAR advances pointer LD A,C ; fetch back character to A. SUB $E6 ; subtract lowest command 'LIST' JR C,<A href="#L07E5">L07E5</a> ; back if not a command to E-L-ERR ; the loop will eventually find the newline ; and the original error point will not be ; altered. LD C,A ; place reduced character in C. LD HL,<A href="#L0752">L0752</a> ; set HL to offset table ADD HL,BC ; add the one-byte offset LD C,(HL) ; fetch the offset from table ADD HL,BC ; add to form address of parameters. JR <A href="#L080C">L080C</a> ; forward to GET-PARAM ; ------------------------ ; THE <b><font color=#333388>'MAIN SCANNING LOOP'</font></b> ; ------------------------ ; entered at GET-PARAM after first instruction. <a name="L0A19"></a>;; <b>SCAN-LOOP</b> L0809: LD HL,($401A) ; T_ADDR ; --> Entry Point. <a name="L080C"></a>;; <b>GET-PARAM</b> L080C: LD A,(HL) ; get parameter from syntax table. INC HL ; point to next one. LD ($401A),HL ; initialize or update T_ADDR LD BC,$0809 ; pre-load the machine stack with the PUSH BC ; return address SCAN-LOOP above. LD C,A ; copy parameter entry to C for later. RLA ; test bit 7 JR C,<A href="#L0826">L0826</a> ; forward to SEPARATOR if inverted. LD HL,<A href="#L0836">L0836</a> ; base address of command class table. LD B,$00 ; prepare to index. ADD HL,BC ; add the command class 0 - 6 LD C,(HL) ; fetch the addressed byte to C ADD HL,BC ; compute starting address of routine. PUSH HL ; push the address on the machine stack. CALL <A href="#L001A">L001A</a> ; routine GET-CHAR advances character position ; and resets the zero flag - see later. RET ; >> an indirect jump to the COMMAND CLASS ; routine. ; <font color=#9900FF>Note.</font> HL addresses the next non-space ; character e.g. the variable in LET I = 1 ; the non-space character is in A ; ---------------------- ; THE <b><font color=#333388>'SEPARATOR'</font></b> BRANCH ; ---------------------- ; branch to here if the parameter has bit seven set. <a name="L0826"></a>;; <b>SEPARATOR</b> L0826: CALL <A href="#L001A">L001A</a> ; get character in A CP $D5 ; compare to the token 'THEN' JR NZ,<A href="#L0831">L0831</a> ; forward if another character to SEP-1. SET 7,(IY+$19) ; else update FLAGX back to K mode <a name="L0831"></a>;; <b>SEP-1</b> L0831: CP C ; compare with expected token/character JR NZ,<A href="#L08AE">L08AE</a> ; forward if no match to set X-PTR ; using INS-ERR RST 20H ; else step past a correct character. RET ; return >> ; (to SCAN-LOOP) ; ------------------------- ; THE <b><font color=#333388>'COMMAND CLASS'</font></b> TABLE ; ------------------------- <a name="L0836"></a>;; <b>TAB-CLASS</b> L0836: DEFB <A href="#L0855">L0855</a> - $ ; $1F offset to class-0 $0855 DEFB <A href="#L086A">L086A</a> - $ ; $33 offset to class-1 $086A DEFB <A href="#L0885">L0885</a> - $ ; $4D offset to class-2 $0885 DEFB <A href="#L0850">L0850</a> - $ ; $17 offset to class-3 $0850 DEFB <A href="#L089E">L089E</a> - $ ; $64 offset to class-4 $089E DEFB <A href="#L0856">L0856</a> - $ ; $1B offset to class-5 $0856 DEFB <A href="#L08A8">L08A8</a> - $ ; $6C offset to class-6 $08A8 ; -------------------------- ; THE <b><font color=#333388>'CHECK END'</font></b> SUBROUTINE ; -------------------------- <a name="L083D"></a>;; <b>CHECK-END</b> L083D: BIT 7,(IY+$01) ; check FLAGS - checking syntax ? RET NZ ; return if running program. POP BC ; else drop the return address. <a name="L0843"></a>;; <b>CH-END-2</b> L0843: LD A,(HL) ; fetch character from CH_ADD address <a name="L0844"></a>;; <b>CH-END-3</b> L0844: CP $76 ; compare to carriage return. CALL NZ,<A href="#L08AE">L08AE</a> ; routine INS-ERR if not disturbing the ; accumulator. <a name="L0849"></a>;; <b>SEE-BELOW</b> L0849: LD A,(HL) ; reload character again. ; and continue... ; ------------------------- ; THE <b><font color=#333388>'REM'</font></b> COMMAND ROUTINE ; ------------------------- ; The REM command compares each character until a newline is encountered. ; However this is a class 5 routine so the initial accumulator value will ; be zero (from the BC test) and not the character following REM. ; A line consisting of a single REM will have the newline skipped and if no ; $76 is encountered in the binary line number then the following line will ; be skipped also as in ; 10 REM ; 20 PRINT "THIS IS NOT HERE" ; The command address should be that of the previous instruction L0849 as the ; accumulator has been disturbed. <a name="L084A"></a>;; <b>REM</b> L084A: CP $76 ; compare with newline. RET Z ; return with newline. RST 20H ; NEXT-CHAR JR <A href="#L084A">L084A</a> ; loop back to REM until newline found. ; ----------------------------------- ; THE <b><font color=#333388>'COMMAND CLASSES - 00, 03 & 05'</font></b> ; ----------------------------------- ; these three commands always terminate a sequence of parameters and ; are followed by the address of a routine. <a name="L0850"></a>;; <b>CLASS-03</b> L0850: CP $76 ; check for carriage return CALL NZ,<A href="#L08A8">L08A8</a> ; else look for optional number using CLASS-06 ; e.g. RUN & RUN 100 ; return and continue through other two classes. <a name="L0855"></a>;; <b>CLASS-00</b> L0855: CP A ; set the zero flag to invoke CHECK-END later. ; this class has no operands e.g. CONTINUE. <a name="L0856"></a>;; <b>CLASS-05</b> L0856: POP BC ; drop the looping address - last in sequence. CALL Z,<A href="#L083D">L083D</a> ; routine CHECK-END if zero flag set. ; (classes 03 and 00) EX DE,HL ; save HL in DE (original CH_ADD) LD HL,($401A) ; fetch table address from T_ADDR LD C,(HL) ; low byte to C INC HL ; LD B,(HL) ; high byte to B EX DE,HL ; bring back the original character address <a name="L0862"></a>;; <b>JUMP-BC</b> L0862: PUSH BC ; push routine address on machine stack LD BC,($4022) ; load value of last expression from RESULT LD A,B ; test the value OR C ; for zero. RET ; jump to the command routine. ; with HL pointing at original CH_ADD ; DE pointing to T_ADDR ; BC holding parameter ; --------------------------------------- ; THE <b><font color=#333388>'COMMAND CLASSES - 01, 02, 04 & 06'</font></b> ; --------------------------------------- ; the first routine is for LET or INPUT. <a name="L086A"></a>;; <b>CLASS-01</b> L086A: CALL <A href="#L0D14">L0D14</a> ; routine ALPHA tests the character. JR NC,<A href="#L08AE">L08AE</a> ; forward to INS-ERR if character not A-Z. BIT 7,(IY+$01) ; test FLAGS - the syntax bit. JP Z,<A href="#L0AAD">L0AAD</a> ; jump forward to LOOK-VARS if checking syntax. ; continue in runtime LD ($4020),HL ; save address of destination variable ; in BASIC line in DEST system variable. RES 7,(IY+$01) ; signal to FLAGS that syntax is being checked. CALL <A href="#L0AAD">L0AAD</a> ; routine LOOK-VARS. SET 7,(IY+$01) ; set FLAGS back to 'running program' status. RET ; return (to SCAN-LOOP). ; ------------------------------ ; used only for LET - an expression of the correct type must be present. <a name="L0885"></a>;; <b>CLASS-02</b> L0885: POP BC ; drop the looping address as CLASS-02 is the ; last in a sequence of parameters. It is ; relevant only to the LET command. LD B,(IY+$01) ; load B with value of FLAGS. ; (runtime input joins here with FLAGX in B instead of FLAGS) ; --------------------------- ; THE <b><font color=#333388>'FETCH A VALUE'</font></b> SECTION ; --------------------------- <a name="L0889"></a>;; <b>VAL-FETCH</b> L0889: PUSH BC ; preserve value of FLAGS (or FLAGX if input) RST 28H ; SCAN-CALC evaluates the expression ; to be assigned setting the result type flag. POP DE ; restore the pre-evaluation copy of the ; flag register to D. LD BC,<A href="#L0C3D">L0C3D</a> ; the address of the LET routine is pushed on ; the machine stack. LD A,($4001) ; fetch the post-evaluation FLAGS to A BIT 7,A ; test the syntax bit. JR NZ,<A href="#L0862">L0862</a> ; back in runtime to JUMP-BC and then LET ; if checking syntax. XOR D ; exclusive or the two flags AND $40 ; AND 01000000 to isolate the type bit. CALL NZ,<A href="#L08AE">L08AE</a> ; routine INS-ERR inserts the error position ; when they are not the same type. JR <A href="#L0843">L0843</a> ; back to CH-END-2 to consider lesser errors ; and advance to end of line. ; ------------------------------ ; FOR, NEXT, DIM - HL points to variable in BASIC line, A holds the character <a name="L089E"></a>;; <b>CLASS-04</b> L089E: LD ($4020),HL ; set system variable DEST from HL. CALL <A href="#L0D14">L0D14</a> ; routine ALPHA checks the character. JR NC,<A href="#L08AE">L08AE</a> ; forward to INS-ERR if not A-Z. RST 18H ; NXT-CH-SP advances character address. RET ; return to SCAN-LOOP >> ; ------------------------------ ; a mandatory INTEGER expression must follow. e.g. GO TO 100 <a name="L08A8"></a>;; <b>CLASS-06</b> L08A8: RST 28H ; SCAN-CALC evaluates expression. BIT 6,(IY+$01) ; test FLAGS - numeric result ? RET NZ ; return if numeric. ; ----------------------------- ; THE <b><font color=#333388>'INSERT ERROR'</font></b> SUBROUTINE ; ----------------------------- <a name="L08AE"></a>;; <b>INS-ERR</b> L08AE: LD A,($4015) ; check that error pointer X_PTR OR (IY+$16) ; contains zero. RET NZ ; return if there is already an error LD ($4015),HL ; else place error address at X-PTR RET ; return. ; ------------------------ ; THE <b><font color=#333388>'IF'</font></b> COMMAND ROUTINE ; ------------------------ <a name="L08B9"></a>;; <b>IF</b> L08B9: JR NZ,<A href="#L08C1">L08C1</a> ; if expression is TRUE forward to IF-1 BIT 7,(IY+$01) ; test FLAGS - checking syntax ? JR NZ,<A href="#L084A">L084A</a> ; back to REM to ignore rest of the line ; in runtime. ; - else continue and check the syntax of the rest of the line. <a name="L08C1"></a>;; <b>IF-1</b> L08C1: JP <A href="#L07E8">L07E8</a> ; jump back to LINE-SCAN to execute what ; follows the 'THEN' ; ------------------------- ; THE <b><font color=#333388>'FOR'</font></b> COMMAND ROUTINE ; ------------------------- ; for example, FOR X = 1 TO 10 ; There is no step or direction. ; The body of the loop is always entered at least once - even if the initial ; value exceeds the limit. ; The ZX81 and ZX Spectrum adhered more closely to the ANS X3.60 1978 BASIC ; standard. <a name="L08C4"></a>;; <b>FOR</b> L08C4: PUSH BC ; save the start value. CALL <A href="#L08A8">L08A8</a> ; routine CLASS-06 evaluates LIMIT ; expression. POP BC ; start value back to BC CALL <A href="#L083D">L083D</a> ; routine CHECK-END quits if checking ; syntax >> LD HL,($4022) ; fetch limit from RESULT PUSH HL ; save limit CALL <A href="#L0C3D">L0C3D</a> ; routine LET POP BC ; restore limit to BC BIT 7,(IY+$00) ; examine ERR_NR RET Z ; return if not $FF >> PUSH BC ; push the limit value. DEC HL ; point to letter. BIT 7,(HL) ; test bit 7 - is it a FOR-NEXT variable. SET 7,(HL) ; set bit 7 as it is going to be. INC HL ; point to end of value INC HL JR NZ,<A href="#L08EA">L08EA</a> ; skip forward if it is a proper ; for/next variable to FOR-2 LD BC,$0004 ; else an extra 4 bytes are needed. INC HL ; point to start of new space. CALL <A href="#L05D5">L05D5</a> ; routine MAKE-ROOM creates it. ; HL - first, DE- last <a name="L08EA"></a>;; <b>FOR-2</b> L08EA: INC HL ; address limit location POP DE ; retrieve limit value to DE. LD (HL),E ; insert low byte of limit. INC HL LD (HL),D ; and then the high byte INC HL ; point to the looping line cell. LD DE,($4002) ; load DE with the current line from PPC INC DE ; increment as iteration will start from the ; next line at least. LD (HL),E ; insert low byte of line number. INC HL LD (HL),D ; insert high byte of line number. RET ; return. ; -------------------------- ; THE <b><font color=#333388>'NEXT'</font></b> COMMAND ROUTINE ; -------------------------- <a name="L08F9"></a>;; <b>NEXT</b> L08F9: LD HL,($4020) ; fetch address of variable in BASIC from DEST. CALL <A href="#L0B3B">L0B3B</a> ; routine LV-FIND finds the equivalent in the ; variables area and returns the value in HL. BIT 7,(IY+$00) ; test ERR_NR RET Z ; return with error. ; will be 02 - variable not found. ; continue if LV-FIND found the variable - HL contains the value, DE points ; to the high byte of value location. EX DE,HL ; value to DE, address to HL DEC HL ; point to low byte DEC HL ; point to the variable letter. BIT 7,(HL) ; - should have letter mask 111xxxxx JR Z,<A href="#L0921">L0921</a> ; forward to ERROR-01 if not initialized by FOR. ; - NEXT without FOR. INC DE ; increment the integer value ; no step or direction possible. INC HL ; address first location LD (HL),E ; store low byte of value. INC HL ; next LD (HL),D ; store high byte of value. INC HL ; LD C,(HL) ; pick up limit low INC HL ; LD B,(HL) ; and limit high. PUSH BC ; save limit. EX (SP),HL ; limit to HL, pointer to stack. CALL <A href="#L0DCD">L0DCD</a> ; routine no-less compares HL DE ; setting carry if HL is less. POP HL ; retrieve the pointer from the stack. RET C ; return if no more iterations possible >> INC HL ; else address next location. LD C,(HL) ; pick up low byte of line number INC HL ; address next LD B,(HL) ; pick up high byte of looping line. JR <A href="#L0934">L0934</a> ; jump to GOTO to perform another ; iteration ; --- <a name="L0921"></a>;; <b>ERROR-01</b> L0921: RST 08H ; ERROR restart DEFB $00 ; NEXT without FOR ; ------------------------------- ; THE <b><font color=#333388>'RANDOMISE'</font></b> COMMAND ROUTINE ; ------------------------------- ; This command sets the seed to the supplied integer -32767 to 32767. ; In the absence of a parameter the FRAMES counter, related to the time ; the computer has been switched on, is used. <a name="L0923"></a>;; <b>RANDOMISE</b> L0923: JR NZ,<A href="#L0929">L0929</a> ; forward to RAND-1 if parameter is ; not zero. LD BC,($401E) ; else use value of system variable FRAMES. <a name="L0929"></a>;; <b>RAND-1</b> L0929: LD ($401C),BC ; insert value in system variable SEED. RET ; return. ; -------------------------- ; THE <b><font color=#333388>'STOP'</font></b> COMMAND ROUTINE ; -------------------------- <a name="L092E"></a>;; <b>STOP</b> <a name="L092E"></a>;; <b>ERROR-9</b> L092E: RST 08H ; ERROR restart DEFB $08 ; - STOP statement executed. ; ------------------------------ ; THE <b><font color=#333388>'CONTINUE'</font></b> COMMAND ROUTINE ; ------------------------------ <a name="L0930"></a>;; <b>CONTINUE</b> L0930: LD BC,($4017) ; fetch continuing line number from OLDPPC ; and continue into GOTO routine. ; --------------------------- ; THE <b><font color=#333388>'GO TO'</font></b> COMMAND ROUTINE ; --------------------------- <a name="L0934"></a>;; <b>GOTO</b> L0934: LD ($4002),BC ; set PPC to supplied line number. SET 3,(IY+$01) ; update FLAGS - use K cursor. RET ; return. ; ------------------------- ; THE <b><font color=#333388>'RUN'</font></b> COMMAND ROUTINE ; ------------------------- ; The RUN command may have an optional line number that will be passed to ; the GOTO routine before erasing any variables and executing the line ; (or first line after zero). <a name="L093D"></a>;; <b>RUN</b> L093D: CALL <A href="#L0934">L0934</a> ; routine GOTO sets up any supplied line number. JP <A href="#L065B">L065B</a> ; exit via CLEAR to erase variables. ; ---------------------------- ; THE <b><font color=#333388>'GO SUB'</font></b> COMMAND ROUTINE ; ---------------------------- <a name="L0943"></a>;; <b>GOSUB</b> L0943: LD HL,($4002) ; fetch current line from PPC INC HL ; increment the line number EX (SP),HL ; place on machine stack ; PUSH HL ; push what was on the stack back up there. CALL <A href="#L0934">L0934</a> ; routine GOTO sets up a branch to the line ; number. LD BC,$0006 ; and exit by a six-byte memory check. ; -------------------------- ; THE <b><font color=#333388>'TEST ROOM'</font></b> SUBROUTINE ; -------------------------- ; The ZX80 dates from the days when RAM chips cost a fortune and it came with ; only 1K of RAM, 1024 bytes. ; The screen could show 768 characters and to economize it is dynamic and ; initialized to a single newline ($76) by CLS. The TEST-ROOM routine has to ; allow for enough newlines to expand down to the bottom line and a few extra ; for the report codes "0/9999". ; The second entry point is from PRINT-A and the character is similarly ; in H and the line number in L. <a name="L094F"></a>;; <b>TEST-ROOM</b> L094F: LD HL,($4010) ; fetch DF_END last location before ; spare memory. ADD HL,BC ; add the supplied overhead. EX DE,HL ; save the result in DE. LD HL,($4025) ; SPOSN-Y to L gives 24 - number ; of screen lines used so far. LD H,A ; preserve the accumulator in H <a name="L0958"></a>;; <b>TEST-RM-2</b> L0958: LD A,$13 ; load A with 19 ADD A,L ; add to L to give the number of bytes ; required to fill rest of screen with ; newlines - plus a bit extra. LD L,A ; put result in L. LD A,H ; restore the accumulator. LD H,$00 ; set H to zero. ADD HL,DE ; add this extra screen allowance ; to the previous result. SBC HL,SP ; subtract the stack pointer. RET C ; return if the stack pointer is ; above the estimate. All is well. ; <a name="L0963"></a>;; <b>ERROR-4</b> L0963: RST 08H ; ERROR restart DEFB $03 ; No room ; ---------------------------- ; THE <b><font color=#333388>'RETURN'</font></b> COMMAND ROUTINE ; ---------------------------- ; As with all commands, there is only one value on the machine stack during ; command execution. This is the return address. ; Above the machine stack is the gosub stack that contains a line number ; (only one statement per line). <a name="L0965"></a>;; <b>RETURN</b> L0965: POP HL ; drop the return address clearing the stack. POP BC ; drop a line number off the gosub stack. PUSH HL ; restore the machine stack. LD A,B ; test high byte of line number. CP $3F ; against the gosub stack end-marker. JR NZ,<A href="#L0934">L0934</a> ; back to GOTO if a valid line number. POP HL ; else collapse the machine stack. PUSH BC ; push the end-marker. PUSH HL ; restore the machine stack. <a name="L0972"></a>;; <b>ERROR-07</b> RST 08H ; ERROR restart DEFB $06 ; RETURN with no corresponding GO SUB. ; --------------------------- ; THE <b><font color=#333388>'PRINT'</font></b> COMMAND ROUTINE ; --------------------------- <a name="L0972"></a>;; <b>PRINT</b> L0972: LD A,(HL) ; fetch the character CP $76 ; compare to NEWLINE JP Z,<A href="#L071B">L071B</a> ; back to PRINT-CR if so. <a name="L0978"></a>;; <b>PR-POSN-1</b> L0978: SUB $D8 ; subtract ',' ; (';' gives -1 and carry set) ADC A,$00 ; convert the two separators to zero. JR Z,<A href="#L0991">L0991</a> ; forward to PR-POSN-2 with ';' and ',' RST 28H ; else SCAN-CALC evaluates expression. CALL <A href="#L06F1">L06F1</a> ; routine PRINT-ITEM prints it. CALL <A href="#L001A">L001A</a> ; routine GET-CHAR gets following character. SUB $D8 ; compare with ',' and test for ADC A,$00 ; terminating separators. JR Z,<A href="#L0991">L0991</a> ; forward to PR-POSN-2 with ';' and ',' CALL <A href="#L083D">L083D</a> ; routine CHECK-END errors with anything else. JP <A href="#L071B">L071B</a> ; jump to PRINT-CR for carriage return. ; --- <a name="L0991"></a>;; <b>PR-POSN-2</b> L0991: CALL NC,<A href="#L0727">L0727</a> ; routine PO-FILL if comma control. RST 20H ; NEXT-CHAR CP $76 ; compare to NEWLINE RET Z ; return if so leaving print position ; unchanged. JR <A href="#L0978">L0978</a> ; else loop back to PR-POSN-1 to consider ; more sequences of positional ; controls and print items. ; --------------------------- ; THE <b><font color=#333388>'INPUT'</font></b> COMMAND ROUTINE ; --------------------------- ; INPUT must be used from a running program. It is not available as a ; direct command. <a name="L099A"></a>;; <b>INPUT</b> L099A: BIT 7,(IY+$03) ; test PPC_hi - will be -2 if a direct command JR NZ,<A href="#L09CF">L09CF</a> ; forward if so, to ERROR-08 POP HL ; discard return address - L0447 LD HL,$4019 ; point to FLAGX SET 5,(HL) ; signal input RES 6,(HL) ; reset so as not to affect combine LD A,($4001) ; fetch FLAGS to A AND $40 ; isolate bit 6 - the result type LD BC,$0002 ; allow two locations for numeric. JR NZ,<A href="#L09B4">L09B4</a> ; skip forward to IN-PR-1 if numeric. LD C,$04 ; allow two extra spaces for quotes. <a name="L09B4"></a>;; <b>IN-PR-1</b> L09B4: OR (HL) ; combine FLAG bit with FLAGX. LD (HL),A ; and place result in FLAGS. RST 30H ; BC-SPACES creates 2/4 locations. RET NC ; return with problems. LD (HL),$76 ; insert a newline at end. LD A,C ; now test C - 2 (num) 4 (str). RRCA ; 1 2 RRCA ; carry 1 JR C,<A href="#L09C2">L09C2</a> ; skip forward with numeric to IN-PR-3 LD (DE),A ; insert initial quote (chr$ 1) at DE DEC HL ; decrease HL pointer LD (HL),A ; insert closing quote. <a name="L09C2"></a>;; <b>IN-PR-3</b> L09C2: DEC HL ; decrease pointer LD (HL),$B0 ; insert cursor inverse 'K' LD A,($4025) ; SPOSN-Y INC A ; allow a blank line LD ($4012),A ; set DF-SZ JP <A href="#L02F7">L02F7</a> ; jump back to ED-COPY ; --- <a name="L09CF"></a>;; <b>ERROR-08</b> L09CF: RST 08H ; ERROR restart DEFB $07 ; INPUT can only be used in a program. ; -------------------------- ; THE <b><font color=#333388>'POKE'</font></b> COMMAND ROUTINE ; -------------------------- <a name="L09D1"></a>;; <b>POKE</b> L09D1: PUSH BC ; save result of first expression. RST 28H ; use SCAN-CALC to evaluate expression ; after the comma. POP DE ; restore destination address. CALL <A href="#L083D">L083D</a> ; routine CHECK-END LD A,($4022) ; RESULT BIT 7,(IY+$00) ; ERR_NR RET Z ; return if error LD (DE),A ; load memory location with A RET ; return ; ---------------------- ; THE <b><font color=#333388>'SCANNING'</font></b> ROUTINE ; ---------------------- ; The scanning routine is a continuation of RST 28. ; The B register has been set to zero as a starting priority. ; The HL register contains the character address CH_ADD. ; The addressed character is in A. <a name="L09E1"></a>;; <b>SCANNING</b> L09E1: LD C,B ; make BC zero - the starting priority ; marker. PUSH BC ; save on machine stack. <a name="L09E3"></a>;; <b>S-LOOP-1</b> L09E3: CALL <A href="#L0D18">L0D18</a> ; routine ALPHANUM JR C,<A href="#L0A24">L0A24</a> ; forward if a variable or digit. to S-VAR-NUM ; now consider negate (-) and perform '$0000 - value' if so. LD BC,$0900 ; prepare priority $09, operation 'subtract' LD D,C ; set DE to $0000 for value to be stacked. LD E,C ; SUB $DC ; subtract the character '-' JR Z,<A href="#L0A17">L0A17</a> ; forward with unary minus to S-PUSH-PO ; now consider 'not' and perform $FFFF - value if so. DEC DE ; set DE to $FFFF for value to be stacked. LD B,$04 ; prepare priority 4, operation still 'subtract' INC A ; test for 'NOT' ? JR Z,<A href="#L0A17">L0A17</a> ; forward with NOT to S-PUSH-PO ; now consider an opening bracket. INC A ; test the character. JR Z,<A href="#L0A1C">L0A1C</a> ; forward with '(' to S-BRACKET ; to evaluate the sub-expression recursively ; using SCANNING. CP $27 ; commencing quote ? JR NZ,<A href="#L0A0E">L0A0E</a> ; forward to S-ABORT if not, as all valid ; possibilities have been exhausted. ; continue to evaluate a string. RES 6,(IY+$01) ; signal string result to FLAGS. INC HL ; step past the opening quote. LD ($4022),HL ; store the string pointer in ; system variable RESULT. <a name="L0A06"></a>;; <b>S-Q-CHAR</b> L0A06: RST 18H ; NXT-CH-SP DEC A ; test for the string terminator. JR Z,<A href="#L0A21">L0A21</a> ; forward to S-CONT if found. >> CP $75 ; [ EDIT ] SHIFT-ENTER JR NZ,<A href="#L0A06">L0A06</a> ; loop back to S-Q-CHAR till terminator found. ; --- ; the branch was here when something unexpected appeared in the expression ; or, if from above, in the string. <a name="L0A0E"></a>;; <b>S-ABORT</b> L0A0E: CALL <A href="#L08AE">L08AE</a> ; routine INS-ERR marks the spot. EXX ; LD BC,$0000 ; this forces the zero priority marker down ; from the stack. ; <font color=#9900FF>Note.</font> just setting B to zero should do. JR <A href="#L0A4C">L0A4C</a> ; forward to S-LOOP to balance and exit ; --- ; the ZX80 juggles with expression components using just the machine stack ; pushing first the value and then the priority/operator beneath. ; As with all ZX computers, provided there is enough memory, an expression of ; unlimited complexity can be evaluated. <a name="L0A17"></a>;; <b>S-PUSH-PO</b> L0A17: PUSH DE ; push the value ($0000 if '-', $FFFF if 'NOT') PUSH BC ; then push the priority and operator. <a name="L0A19"></a>;; <b>SCAN-LOOP</b> L0A19: RST 20H ; NEXT-CHAR advances the character address. JR <A href="#L09E3">L09E3</a> ; back to S-LOOP-1 ; --- <a name="L0A1C"></a>;; <b>S-BRACKET</b> L0A1C: CALL <A href="#L0049">L0049</a> ; routine BRACKET evaluates expression ; inside the brackets checking for ; terminator using SCANNING ; recursively. JR <A href="#L0A37">L0A37</a> ; forward to S-OPERTR ; --- ; the branch was here when the end of a string had been found. <a name="L0A21"></a>;; <b>S-CONT</b> L0A21: RST 18H ; NXT-CH-SP JR <A href="#L0A37">L0A37</a> ; forward to S-OPERTR to consider comparisons ; --- <a name="L0A24"></a>;; <b>S-VAR-NUM</b> L0A24: CP $26 ; compare to 'A' JR C,<A href="#L0A2D">L0A2D</a> ; forward if numeric to S-DIGIT ; present character is alpha CALL <A href="#L0AAD">L0AAD</a> ; routine LOOK-VARS JR <A href="#L0A37">L0A37</a> ; forward to S-OPERTR ; --- <a name="L0A2D"></a>;; <b>S-DIGIT</b> L0A2D: CALL <A href="#L0679">L0679</a> ; routine INT-TO-HL CALL C,<A href="#L08AE">L08AE</a> ; routine INS-ERR with overflow. SET 6,(IY+$01) ; signal numeric result in FLAGS <a name="L0A37"></a>;; <b>S-OPERTR</b> L0A37: CALL <A href="#L001A">L001A</a> ; routine get-char EXX LD BC,$0000 ; prepare zero priority in case not an operator ; in which case at end of expression SUB $DC ; reduce by '-' JR C,<A href="#L0A4C">L0A4C</a> ; forward if less than an operator to S-LOOP CP $0A ; compare to ten. JR NC,<A href="#L0A4C">L0A4C</a> ; forward if higher than nine to S-LOOP ; leaves ten operators -, +, *, /, AND, OR, **, =, >, <. LD C,A ; transfer operation to C, register B is zero. LD HL,<A href="#L0AA3">L0AA3</a> ; address table of priorities. ADD HL,BC ; index into table. LD B,(HL) ; pick up the priority. <a name="L0A4C"></a>;; <b>S-LOOP</b> L0A4C: POP DE ; pop the previous priority/operation LD A,D ; priority to A CP B ; compare with current priority B JR C,<A href="#L0A88">L0A88</a> ; forward to S-TIGHTER if current priority is ; higher ; else this is the correct place in the expression to perform this operation. AND A ; first test for zero priority marker EXX ; RET Z ; return if so, HL is result. >>>>> EXX ; BIT 7,(IY+$01) ; FLAGS JR Z,<A href="#L0A6F">L0A6F</a> ; forward if checking syntax to S-SYNTEST ; but in runtime the operation is performed. LD D,$00 ; prepare to index. LD HL,<A href="#L0D1F">L0D1F</a> ; address the table of operators and addresses. ADD HL,DE ; index twice using the operation code. ADD HL,DE ; as there are two bytes per entry. LD E,(HL) ; pick up low byte of address. INC HL ; next location. LD D,(HL) ; get high byte of address. LD HL,<A href="#L0A7F">L0A7F</a> ; the return address S-INS-VAL EX (SP),HL ; goes to the stack and argument to HL PUSH DE ; now push the address of the routine. LD DE,($4022) ; pick up last value from RESULT RET ; and make an indirect jump to ; the routine. >>>>>>>> ; ------------------------------ <a name="L0A6F"></a>;; <b>S-SYNTEST</b> L0A6F: LD A,E ; get the last operation code CP $0A ; compare to ten - sets carry if numeric RRA ; carry to bit 7 RRA ; carry to bit 6 XOR (IY+$01) ; exclusive or with FLAGS AND $40 ; isolate bit 6 - the result type. EXX ; CALL NZ,<A href="#L08AE">L08AE</a> ; routine INS-ERR if not of same type. EXX ; POP HL ; fetch the last value from machine stack ; >>>>>>>> ; <font color=#9900FF>Note.</font> this is also the return address from mathematical and string ; comparisons, see above, in which case HL will contain the result and BC ; the priority/operation. <a name="L0A7F"></a>;; <b>S-INS-VAL</b> L0A7F: LD ($4022),HL ; place value in system variable RESULT SET 6,(IY+$01) ; signal numeric result to FLAGS JR <A href="#L0A4C">L0A4C</a> ; back to S-LOOP ; --- <a name="L0A88"></a>;; <b>S-TIGHTER</b> L0A88: PUSH DE ; push lower priority LD A,C ; fetch operator BIT 6,(IY+$01) ; test FLAGS JR NZ,<A href="#L0A9A">L0A9A</a> ; forward if numeric to S-NEXT. ADD A,$03 ; augment nos-eql to strs-eql etc. LD C,A ; and put back in C CP $0A ; compare to ten - start of string comparisons EXX ; CALL C,<A href="#L08AE">L08AE</a> ; routine INS-ERR if lower ; a$ * b$ is invalid but so too ; is a$ + b$ (no string concatenation) EXX ; <a name="L0A9A"></a>;; <b>S-NEXT</b> L0A9A: LD HL,($4022) ; fetch RESULT to HL PUSH HL ; push intermediate result PUSH BC ; and then priority/operator EXX ; JP <A href="#L0A19">L0A19</a> ; jump back to SCAN-LOOP ; ------------------------- ; THE <b><font color=#333388>'TABLE OF PRIORITIES'</font></b> ; ------------------------- ; Table of mathematical priorities that dictate, in the absence of brackets, ; the order in which operations are performed. ; unary minus (priority $09) and NOT (priority $04) are handled directly. <a name="L0AA3"></a>;; <b>TAB-PRIO</b> L0AA3: DEFB $06 ; $00 subtract DEFB $06 ; $01 addition DEFB $08 ; $02 multiply DEFB $07 ; $03 division DEFB $03 ; $04 and DEFB $02 ; $05 or DEFB $0A ; $06 to-power DEFB $05 ; $07 nos-eql DEFB $05 ; $08 no-grtr DEFB $05 ; $09 no-less ; -------------------------- ; THE <b><font color=#333388>'LOOK-VARS'</font></b> SUBROUTINE ; -------------------------- <a name="L0AAD"></a>;; <b>LOOK-VARS</b> L0AAD: PUSH HL ; * push pointer to first letter LD HL,$4001 ; address FLAGS RES 5,(HL) ; update FLAGS - signal not a function yet. ; but no use is made of this flag bit. SET 6,(HL) ; update FLAGS - presume a numeric result. RST 18H ; NXT-CH-SP CP $0D ; compare to '$' ? JP Z,<A href="#L0B30">L0B30</a> ;; JUMP forward with match to STRING CP $DA ; compare to '(' ? JP Z,<A href="#L0B2B">L0B2B</a> ;; JUMP forward with match to ARRAY ; that leaves three types of integer plus functions. <a name="L0AC0"></a>;; <b>V-CHAR</b> L0AC0: CALL <A href="#L0D18">L0D18</a> ; routine ALPHANUM JR NC,<A href="#L0AC8">L0AC8</a> ; forward when not alphanumeric to FUNC-LOOP. RST 18H ; fetch NXT-CH-SP. JR <A href="#L0AC0">L0AC0</a> ; loop back to V-CHAR for more. ; --- <a name="L0AD9"></a>;; <b>FUNC-LOOP</b> L0AC8: CP $DA ; compare to '(' ? JR Z,<A href="#L0AD6">L0AD6</a> ; forward with a match to FUNC-SRCH CP $0D ; compare to '$' ? JP NZ,<A href="#L0B35">L0B35</a> ;; JUMP forward if not to V-SYN ; but if this is a string function such as CHR$ then the bracket must follow. RST 18H ; NXT-CH-SP CP $DA ; compare to '(' ? JR NZ,<A href="#L0B27">L0B27</a> ; forward if not to FUNC-ERR. ; This has the correct format for a function and an exact match must now be ; made to one of the entries in the functions table. <a name="L0AD6"></a>;; <b>FUNC-SRCH</b> L0AD6: LD DE,<A href="#L0BC0">L0BC0</a> - 1 ; point to location before TAB-FUNC <a name="L0AD9"></a>;; <b>FUNC-LOOP</b> L0AD9: POP HL ; pop pointer to first character in command PUSH HL ; and push again. <a name="L0ADB"></a>;; <b>FUNC-CHAR</b> L0ADB: LD C,(HL) ; fetch command character to C. CALL <A href="#L0055">L0055</a> ; routine CH-ADD-LP advances CH-ADD ; to next non-space position. INC DE ; increment position in table LD A,(DE) ; fetch table character to A. CP C ; compare with one in command. JR Z,<A href="#L0ADB">L0ADB</a> ; loop back with match to FUNC-CHAR ; e.g. PEEK AND $3F ; cancel any inversion. CP C ; and compare again JR NZ,<A href="#L0AEE">L0AEE</a> ; skip if no match to FUNC-NEXT. LD A,$DA ; load with '(' CP (HL) ; compare to next valid character JR Z,<A href="#L0AF9">L0AF9</a> ; forward with success to FUNC-MTCH. <a name="L0AEE"></a>;; <b>FUNC-NEXT</b> L0AEE: LD A,(DE) ; fetch next character from table. AND A ; test for zero end-marker. JR Z,<A href="#L0B27">L0B27</a> ; forward if at end of table to FUNC-ERR. INC DE ; else increment pointer. RLA ; test for inverted bit. JR NC,<A href="#L0AEE">L0AEE</a> ; loop back to FUNC-NEXT ; until new token found. INC DE ; increment pointer. ; to skip address in table. JR <A href="#L0AD9">L0AD9</a> ; loop back to FUNC-LOOP ; which begins by skipping the ; remaining address byte. ; --- ; A function such as PEEK has been found with the necessary opening bracket. <a name="L0AF9"></a>;; <b>FUNC-MTCH</b> L0AF9: PUSH DE ; save pointer to address within ; table. CALL <A href="#L0049">L0049</a> ; routine BRACKET evaluates an ; expression within brackets in command. ; result in HL POP DE ; retrieve table address pointer. EX (SP),HL ; result to stack, discarding command ; character pointer. LD HL,$4001 ; load with address FLAGS LD A,(DE) ; fetch the last inverted character. XOR (HL) ; XOR with FLAGS AND $40 ; isolate bit 6 - result type. JR NZ,<A href="#L0B27">L0B27</a> ; to FUNC-ERR to insert an error with ; an argument type mismatch. SET 5,(HL) ; update FLAGS signal a function has been found ; but no use is made of this ????? SET 6,(HL) ; default the result type to be numeric. LD A,(DE) ; fetch last character AND $3F ; lose the indicator bits. CP $0D ; is character '$' ? ; i.e. CHR$, STR$ or TL$. JR NZ,<A href="#L0B15">L0B15</a> ; forward with numeric function results ; to FUNC-SYN. RES 6,(HL) ; else set FLAGS to indicate a string ; result is expected. <a name="L0B15"></a>;; <b>FUNC-SYN</b> L0B15: BIT 7,(HL) ; test FLAGS checking syntax? POP HL ; restore RESULT of expression in brackets. RET Z ; return if checking syntax. >> LD HL,<A href="#L0BBA">L0BBA</a> ; else the routine INS-RSLT PUSH HL ; is pushed on the machine stack EX DE,HL ; HL now points to table entry. INC HL ; point to address low byte. LD E,(HL) ; pick up the low byte. INC HL LD D,(HL) ; pick up the high byte. PUSH DE ; push routine address on stack. LD HL,($4022) ; load HL with argument from RESULT ; either integer or string pointer. RET ; indirect jump to routine and then ; to INS-RSLT . ; --- <a name="L0B27"></a>;; <b>FUNC-ERR</b> L0B27: POP HL ; balance stack. JP <A href="#L08AE">L08AE</a> ; jump back to INS-ERR ; ------------------------------ <a name="L0B2B"></a>;; <b>ARRAY</b> L0B2B: CALL <A href="#L0049">L0049</a> ; routine BRACKET evaluates expression JR <A href="#L0B35">L0B35</a> ; skip to V-SYN ; --- <a name="L0B30"></a>;; <b>STRING</b> L0B30: RES 6,(IY+$01) ; FLAGS signal string result. RST 18H ; NXT-CH-SP <a name="L0B35"></a>;; <b>V-SYN</b> L0B35: POP HL ; * restore pointer to first letter BIT 7,(IY+$01) ; check FLAGS RET Z ; return if checking syntax ; but continue in run-time ; also called from NEXT and LET ; HL points to first letter of variable in the command. <a name="L0B3B"></a>;; <b>LV-FIND</b> L0B3B: LD C,(HL) ; C first character INC HL LD A,(HL) ; A second character PUSH HL ; save pointer to character 2 CP $DA ; is second character '(' ? JR NZ,<A href="#L0B5C">L0B5C</a> ; forward if not to LV-ENCODE with strings and ; simple numeric variables. ; an array PUSH BC ; save BC on stack LD BC,($4026) ; fetch character address CH_ADD PUSH BC ; and save that on stack as well. CALL <A href="#L0025">L0025</a> ; routine EVAL-EXPR evaluates the ; expression after the current '(' ; disturbing CH_ADD POP HL ; restore original value of CH_ADD LD ($4026),HL ; and backdate CH_ADD system variable. POP BC ; restore the letter in BC. LD HL,$4000 ; address system variable ERR_NR BIT 7,(HL) ; test if $FF has been disturbed by eval_expr. JR NZ,<A href="#L0B6B">L0B6B</a> ; forward if not to V-RUN. LD (HL),$02 ; else insert the code for subscript error POP HL ; balance the stack RET ; return with error set. >> ; --- ; encode the variable type into bits 5-7 of the letter. <a name="L0B5C"></a>;; <b>LV-ENCODE</b> L0B5C: RES 5,C ; presume type string CP $0D ; is second character '$' ? JR Z,<A href="#L0B6B">L0B6B</a> ; forward if so to V-RUN SET 6,C ; presume long-named numeric. CALL <A href="#L0D18">L0D18</a> ; routine ALPHANUM test second character. JR C,<A href="#L0B6B">L0B6B</a> ; forward if so to V-RUN SET 5,C ; else mark as simple numeric or for/next <a name="L0B6B"></a>;; <b>V-RUN</b> L0B6B: LD HL,($4008) ; point HL to the first variable from VARS. <a name="L0B6E"></a>;; <b>V-EACH</b> L0B6E: LD A,(HL) ; fetch letter/marker AND $7F ; reset bit 7 to allow simple numeric variables ; to match against FOR-NEXT variables. JP Z,<A href="#L0CD0">L0CD0</a> ; if character was $80 then forward to ERROR-02 ; Variable not found. CP C ; else compare to first letter in command JR NZ,<A href="#L0B93">L0B93</a> ; forward if no match to V-NEXT RLA ; rotate A to left and then ADD A,A ; double to test bits 5 and 6. JP M,<A href="#L0BA4">L0BA4</a> ; forward to STK-VAR with ; all single letter numeric variables ; including for/next and arrays. JR NC,<A href="#L0BB8">L0BB8</a> ; forward to STR-RSLT with string. ; that leaves long-named variables (mask 010xxxxx) ; that have to be matched in full. POP DE ; take a copy of pointer. PUSH DE ; to 2nd character in BASIC area. PUSH HL ; save 1st letter pointer in vars area. <a name="L0B81"></a>;; <b>V-MATCHES</b> L0B81: INC HL ; point to next vars character. LD A,(DE) ; fetch each BASIC char in turn. INC DE ; advance BASIC pointer CP (HL) ; compare to character in variable JR Z,<A href="#L0B81">L0B81</a> ; back if the same to V-MATCHES OR $80 ; try a match on inverted character. CP (HL) ; compare to variable JR NZ,<A href="#L0B92">L0B92</a> ; forward to V-GET-PTR without full ; match. LD A,(DE) ; check that the end of name in BASIC ; has been reached. CALL <A href="#L0D18">L0D18</a> ; routine ALPHANUM checks that no ; more letters follow. JR NC,<A href="#L0B9B">L0B9B</a> ; forward to V-FOUND-1 with a full ; match on an inverted long name. ; else continue the search <a name="L0B92"></a>;; <b>V-GET-PTR</b> L0B92: POP HL ; fetch the pointer. <a name="L0B93"></a>;; <b>V-NEXT</b> L0B93: PUSH BC ; save B and C CALL <A href="#L0624">L0624</a> ; routine NEXT-ONE points DE at next ; variable EX DE,HL ; switch pointers. POP BC ; retrieve B and C. JR <A href="#L0B6E">L0B6E</a> ; back for another search to V-EACH. ; --- <a name="L0B9B"></a>;; <b>V-FOUND-1</b> L0B9B: POP DE ; drop saved var pointer <a name="L0B9C"></a>;; <b>V-FOUND-2</b> L0B9C: POP DE ; drop pointer to second character <a name="L0B9D"></a>;; <b>V-FOUND-3</b> L0B9D: INC HL ; advance to value. LD E,(HL) ; fetch low byte to E INC HL ; LD D,(HL) ; fetch high byte to D. EX DE,HL ; value to HL JR <A href="#L0BBA">L0BBA</a> ; forward to INS-RSLT ; --- ; simple 011xxxxx, array 101xxxxx, for/next 111xxxxx <a name="L0BA4"></a>;; <b>STK-VAR</b> L0BA4: JR C,<A href="#L0B9C">L0B9C</a> ; back to V-FOUND-2 above with simple ; and FOR/NEXT variables. <a name="L0BB8"></a>;; <b>SV-ARRAYS</b> EX (SP),HL ; save pointer to letter on stack discarding ; the second letter pointer LD HL,($4022) ; fetch argument within brackets from RESULT RLC H ; test the high byte. POP DE ; retrieve pointer to letter JR NZ,<A href="#L0BBE">L0BBE</a> ; forward to ERROR-03 subscript error ; if subscript > 255 INC DE ; point to dimensions value - 1 byte LD A,(DE) ; fetch the max subscription CP L ; compare to low byte of argument. JR C,<A href="#L0BBE">L0BBE</a> ; forward if higher than max subscription ; to ERROR-03. ADD HL,HL ; double the subscript 0 - 510 ADD HL,DE ; add to variable pointer ; now point to location before required cell. ; if the first element is 0 then still pointing ; at the max subscription byte. JR <A href="#L0B9D">L0B9D</a> ; back to V-FOUND-3 above. ; --- ; string type mask 100xxxxx <a name="L0BB8"></a>;; <b>STR-RSLT</b> L0BB8: POP DE ; drop pointer to var. INC HL ; advance to first character of string. <a name="L0BBA"></a>;; <b>INS-RSLT</b> L0BBA: LD ($4022),HL ; insert value/pointer into RESULT RET ; return. ; --- <a name="L0BBE"></a>;; <b>ERROR-03</b> L0BBE: RST 08H ; ERROR restart DEFB $02 ; subscript error ; ------------------------------ ; THE <b><font color=#333388>'INTEGRAL FUNCTIONS TABLE'</font></b> ; ------------------------------ ; Table of functions to be parsed and addresses. ; Parsed by LOOK-VARS. ; Inversion is with $80 (string argument) ; and with $CO (numeric argument). ; The TL$, "Truncate Left string", of "CABBAGE" is "ABBAGE". <a name="L0BC0"></a>;; <b>TAB-FUNC</b> L0BC0: DEFB $35,$2A,$2A,$F0 ; PEEK (+$C0) DEFW <A href="#L0C24">L0C24</a> ; $0C24 DEFB $28,$2D,$37,$CD ; CHR$ (+$C0) DEFW <A href="#L0C28">L0C28</a> ; $0C28 DEFB $28,$34,$29,$AA ; CODE (+$80) DEFW <A href="#L0C24">L0C24</a> ; $0C24 DEFB $37,$33,$E9 ; RND (+$C0) DEFW <A href="#L0BED">L0BED</a> ; $OBED DEFB $39,$31,$8D ; TL$ (+$80) DEFW <A href="#L0C38">L0C38</a> ; $0C38 DEFB $3A,$38,$F7 ; USR (+$C0) DEFW <A href="#L06F0">L06F0</a> ; $06F0 DEFB $38,$39,$37,$CD ; STR$ (+$C0) DEFW <A href="#L0C10">L0C10</a> ; $0C10 DEFB $26,$27,$F8 ; ABS (+$C0) DEFW <A href="#L0DF2">L0DF2</a> ; $0DF2 DEFB $00 ; zero end-marker ; ------------------ ; THE <b><font color=#333388>'RND'</font></b> FUNCTION ; ------------------ ; e.g. LET LOTTERYNUMBER = RND (49) produces a random number in the range ; 1 to 49. ; the routine has two stages - ; First the seed is fetched and manipulated in such a way that it cycles through ; every value between 0 and 65535 in a pseudo-random way before repeating the ; sequence. If the seed fetched is zero it is set to 65536-77. ; The multiplicand used is 77 and any overflow is subtracted from the ; register result. <a name="L0BED"></a>;; <b>RND</b> L0BED: PUSH HL ; * save the integer parameter e.g. 49. LD HL,($401C) ; fetch the 'seed' from SEED. LD DE,$004D ; place 77 in DE LD A,H ; test the seed OR L ; for value zero JR Z,<A href="#L0C03">L0C03</a> ; forward if zero. CALL <A href="#L0D55">L0D55</a> ; routine MULT16 multiplies seed by 77 ; BC contains zero or overflow AND A ; clear carry flag. SBC HL,BC ; subtract any overflow from lower 16 bits JR NC,<A href="#L0C05">L0C05</a> ; forward if no carry to RND-3 INC HL ; increase seed value. JR <A href="#L0C05">L0C05</a> ; forward to RND-3 ; --- <a name="L0C03"></a>;; <b>RND-2</b> L0C03: SBC HL,DE ; form number $FFB3 if seed is zero. <a name="L0C05"></a>;; <b>RND-3</b> L0C05: LD ($401C),HL ; store new value of SEED ; now multiply the new seed by the argument to give result-1 in BC. POP DE ; * restore argument CALL <A href="#L0D55">L0D55</a> ; routine MULT16 multiplies HL by DE ; returning in BC, for the example, 0-48 LD H,B ; transfer BC LD L,C ; to HL - the result register. INC HL ; increment - make range start with 1. RET ; return ; ------------------- ; THE <b><font color=#333388>'STR$'</font></b> FUNCTION ; ------------------- ; the function produces a string comprising the characters that would appear ; if the numeric argument were printed. ; So seven characters e.g. "-10000" terminated by the null character ($01) ; is the maximum amount of characters required. ; <font color=#9900FF>Note.</font> that for this reason the ZX80, unlike the ZX81 and ZX Spectrum, is able ; to have four tabstops across the 32 character screen. <a name="L0C10"></a>;; <b>str$</b> L0C10: EXX LD BC,$0007 ; 7 characters required at most. RST 30H ; routine BC-SPACES JR NC,<A href="#L0C34">L0C34</a> ; forward to NULL-STR if not enough ; memory. PUSH DE ; * save start of new space EXX ; switch in other set LD B,H ; transfer argument to BC LD C,L ; register. CALL <A href="#L06A1">L06A1</a> ; OUT-NUM-1 prints at this DE in WKG Space. EXX ; switch back LD A,$01 ; prepare the terminating '"' LD (DE),A ; and place at end of string. <a name="L0C22"></a>;; <b>POP-RET</b> L0C22: POP HL ; * restore result pointer. RET ; return. ; ------------------------------- ; THE <b><font color=#333388>'CODE'</font></b> AND 'PEEK' FUNCTIONS ; ------------------------------- ; Two functions in one subroutine. ; CODE with HL pointing to start of string. ; and also, ; PEEK with HL pointing to a memory address. ; The return value is in HL. <a name="L0C24"></a>;; <b>CODE</b> <a name="L0C24"></a>;; <b>PEEK</b> L0C24: LD L,(HL) ; parameter is in HL. LD H,$00 ; RET ; return with result in HL. ; ------------------- ; THE <b><font color=#333388>'CHR$'</font></b> FUNCTION ; ------------------- ; this function returns the null-terminated single-character string that ; corresponds to the integer argument e.g. CHR$(38) returns "A". <a name="L0C28"></a>;; <b>chr$</b> L0C28: LD BC,$0002 ; two locations required. LD A,L ; character to A. RST 30H ; BC-SPACES creates two locations ; in WORKSPACE JR NC,<A href="#L0C34">L0C34</a> ; forward to NULL-STR if no room. <a name="L0C2F"></a>;; <b>NULL-PTR</b> L0C2F: LD (HL),$01 ; insert the '"' terminator at last new location DEC HL ; decrease the pointer. LD (HL),A ; insert the character. RET ; return with HL pointing to string. ; --- <a name="L0C34"></a>;; <b>NULL-STR</b> L0C34: LD HL,<A href="#L0C2F">L0C2F</a> + 1 ; point to the null string at NULL-PTR + 1 ; in the above code. RET ; return. ; ------------------ ; THE <b><font color=#333388>'TL$'</font></b> FUNCTION ; ------------------ ; This limited string slicing function returns the tail of a string starting ; at the second character and the null string otherwise. ; It requires no string workspace. <a name="L0C38"></a>;; <b>tl$</b> L0C38: LD A,(HL) ; fetch first character of string DEC A ; decrement it. RET Z ; return if was CHR$ 1 - the null string. INC HL ; else increase the string pointer RET ; return with HL pointing at result. ; ----------------- ; THE <b><font color=#333388>'LET'</font></b> ROUTINE ; ----------------- ; This subroutine is called from the FOR command and the CLASS-02 routine ; to create the variable. <a name="L0C3D"></a>;; <b>LET</b> L0C3D: BIT 7,(IY+$00) ; test ERR_NR RET Z ; return if not $FF ; proceed if no errors so far. PUSH BC ; save start val LD HL,($4020) ; fetch location of letter in BASIC from DEST CALL <A href="#L0B3B">L0B3B</a> ; routine LV-FIND will set error LD HL,$4000 ; ERR_NR LD A,(HL) CP $02 ; compare to 2 - subscript out of range JR Z,<A href="#L0C22">L0C22</a> ; back to POP-RET if so >>> ; continue with variable not found or OK. RLA ; test for $FF?? BIT 6,(IY+$01) ; test bit 6 FLAGS - affects zero flag only. ; zero if string NZ if numeric JR C,<A href="#L0C93">L0C93</a> ; forward if error was $FF to L-EXISTS ; continue if variable does not exist. LD (HL),$FF ; cancel the error as variable will be created. JR Z,<A href="#L0CA3">L0CA3</a> ; forward to L-STRING with string var. ; continue with numeric INTEGER variable LD HL,($4020) ; pick up destination from DEST LD BC,$0002 ; set default space for integer contents ; will be 3 including letter <a name="L0C62"></a>;; <b>L-EACH-CH</b> L0C62: INC BC ; pre-increment character count. INC HL ; increment character pointer in BASIC or ; workspace. LD A,(HL) ; fetch the character. CALL <A href="#L0D18">L0D18</a> ; routine ALPHANUM check if "[0-Z]" JR C,<A href="#L0C62">L0C62</a> ; loop back if so to L-EACH-CH CP $DA ; is character '(' ? JR Z,<A href="#L0CD0">L0CD0</a> ; forward if so to ERROR-02 - var not found. ; e.g. perhaps a function has been misspelled. RST 30H ; BC-SPACES creates room for new INTEGER ; variable at D-FILE - 1, the variables ; end-marker. JR NC,<A href="#L0C22">L0C22</a> ; back to POP-RET if not enough room PUSH DE ; save first new location *** LD HL,($4020) ; fetch DEST the pointer to letter in command DEC BC ; reduce count by DEC BC ; the three bytes DEC BC ; for simple integer. DEC DE ; point to destination LD A,B ; check if this is a one-character OR C ; variable name from reduced count. LD A,$40 ; prepare mask 010xxxxx JR Z,<A href="#L0C87">L0C87</a> ; forward to L-SINGLE if is simple numeric. LDIR ; else copy all but one characters of name. LD A,(HL) ; fetch last character OR $80 ; invert it LD (DE),A ; place at last destination LD A,$60 ; prepare mask 011xxxxx <a name="L0C87"></a>;; <b>L-SINGLE</b> L0C87: POP HL ; restore first new location *** CALL <A href="#L0CB9">L0CB9</a> ; routine L-MASK inserts masked letter. EX DE,HL ; DEC DE ; ; and continue to initialize variable contents. ; this branch is taken from below to overwrite contents. <a name="L0C8D"></a>;; <b>L-NUMERIC</b> L0C8D: POP HL ; restore variable value EX DE,HL ; HL points last location LD (HL),D ; insert high byte. DEC HL ; decrement the pointer. LD (HL),E ; and insert low-byte value RET ; return. with HL addressing the value. >>>> ; --- <a name="L0C93"></a>;; <b>L-EXISTS</b> L0C93: JR NZ,<A href="#L0C8D">L0C8D</a> ; back to L-NUMERIC to overwrite variable ; if numeric type. POP HL ; restore string CALL <A href="#L0CA4">L0CA4</a> ; routine L-LENGTH evaluates length of OLD ; string LD HL,($4022) ; fetch string pointer from RESULT DEC HL ; decrement to point to letter. CALL <A href="#L0624">L0624</a> ; routine NEXT-ONE calculate space to delete JP <A href="#L0666">L0666</a> ; routine RECLAIM-2 ; now continue into L-STRING to evaluate length of new string. ; --- <a name="L0CA3"></a>;; <b>L-STRING</b> L0CA3: POP HL ; restore pointer to contents. <a name="L0CA4"></a>;; <b>L-LENGTH</b> L0CA4: LD A,$01 ; the search will be for the quote character. LD BC,$0001 ; initialize length to one. <a name="L0CA9"></a>;; <b>L-COUNT</b> L0CA9: CP (HL) ; is addressed character null ? INC HL ; increase pointer. INC BC ; increase length. JR NZ,<A href="#L0CA9">L0CA9</a> ; loop back to L-COUNT till terminating ; quote found. PUSH HL ; save pointer to end - null terminator. RST 30H ; routine BC-SPACES creates room at end. EX DE,HL ; transfer end to DE. POP HL ; retrieve pointer to null terminator in E-LINE. RET NC ; return if no room was available. LDDR ; else copy string to the variables area. EX DE,HL ; HL now points to letter -1 INC HL ; adjust LD A,$A0 ; prepare mask %10100000 <a name="L0CB9"></a>;; <b>L-MASK</b> L0CB9: EX DE,HL ; save variable pointer in DE. LD HL,($4020) ; fetch destination in prog/e-line area ; from system variable DEST XOR (HL) ; XOR mask with the letter. ; <font color=#9900FF>Note.</font> All letters have bit 5 set. The ; preparation of masks must accommodate this. EX DE,HL ; variable pointer to HL, PUSH AF ; save masked letter CALL <A href="#L0D0D">L0D0D</a> ; routine REC-V80 reclaims ; the previous $80 variables end-marker. POP AF ; pop the letter. DEC HL ; point to the letter in the variables area. ; which is now one location lower than it was ; a moment ago. LD (HL),A ; insert masked letter. LD HL,($400C) ; use D_FILE value LD ($400A),HL ; to update new E_LINE DEC HL ; step back. LD (HL),$80 ; and insert the new variable $80 end-marker. RET ; return. ; --- <a name="L0CD0"></a>;; <b>ERROR-02</b> L0CD0: POP HL ; RST 08H ; ERROR restart DEFB $01 ; variable name not found. ; ------------------------- ; THE <b><font color=#333388>'DIM'</font></b> COMMAND ROUTINE ; ------------------------- ; This routine creates a one-dimensional numeric array with up to ; 256 subscripts. Each is initialized to the integer zero. ; <font color=#9900FF>Note.</font> array subscripts begin at zero. On later ZX computers subscripts began ; at 1 and there were no limits to the dimensions and subscripts other than ; memory. <a name="L0CD3"></a>;; <b>DIM</b> L0CD3: AND B ; check high byte of parameter. ; a maximum of 255 subscripts possible. JP NZ,<A href="#L0BBE">L0BBE</a> ; back to ERROR-03 - subscript error. PUSH BC ; save max subscript LD H,B ; transfer LD L,C ; to HL. INC HL ; increment to make range 1-256 from 0-255 INC HL ; increment for letter and subscript byte ADD HL,HL ; double - allocates two bytes per integer ; and two for the letter and subscript. LD B,H ; transfer count LD C,L ; to BC RST 30H ; BC-SPACES JP NC,<A href="#L0C22">L0C22</a> ; back to POP-RET if out of memory DEC HL ; point to last new location LD D,H ; transfer to DE LD E,L ; - the destination. DEC DE ; make DE one less than source. DEC BC ; reduce count DEC BC ; by two. LD (HL),$00 ; insert a zero at source. LDDR ; block fill locations with zero. POP BC ; restore number of subscripts LD (HL),C ; and place in location before data. LD A,$80 ; prepare mask %100 JR <A href="#L0CB9">L0CB9</a> ; back to L-MASK ; --------------------- ; THE <b><font color=#333388>'RESERVE'</font></b> ROUTINE ; --------------------- ; A continuation of the BC-SPACES RESTART. ; the number of bytes required is on the machine stack. <a name="L0CF3"></a>;; <b>RESERVE</b> L0CF3: LD HL,($400A) ; fetch start of WKG Space from E_LINE PUSH HL ; preserve location. LD HL,($400C) ; fetch location after WKG Space from D_FILE DEC HL ; point to last byte of WKG space. CALL <A href="#L05D5">L05D5</a> ; routine MAKE-ROOM creates the space after ; last byte sliding D-FILE up and updating ; D_FILE, DF_EA and DF_END INC HL ; increase address INC HL ; by two bytes POP BC ; retrieve E_LINE which may have been updated ; by pointers LD ($400A),BC ; restore E_LINE POP BC ; restore the number of bytes required. EX DE,HL ; switch - DE points to first INC HL ; make HL point to last new byte SCF ; signal success RET ; return ; -------------------------------------- ; THE <b><font color=#333388>'RECLAIM THE EDIT LINE'</font></b> SUBROUTINE ; -------------------------------------- ; Interestingly, Hugo Davenport refers to this subroutine in the manual ; by its Nine Tiles source code label X_TEMP. ; The second entry point deletes the old variables end-marker when creating ; a new variable immediately after this position. <a name="L0D0A"></a>;; <b>REC-EDIT</b> L0D0A: LD HL,($400C) ; D_FILE <a name="L0D0D"></a>;; <b>REC-V80</b> L0D0D: LD DE,($400A) ; E_LINE JP <A href="#L0663">L0663</a> ; RECLAIM-1 ; ---------------------- ; THE <b><font color=#333388>'ALPHA'</font></b> SUBROUTINE ; ---------------------- <a name="L0D14"></a>;; <b>ALPHA</b> L0D14: CP $26 ; compare to 'A' JR <A href="#L0D1A">L0D1A</a> ; forward to ALPHA-2 to compare ; against 'Z' ; ------------------------- ; THE <b><font color=#333388>'ALPHANUM'</font></b> SUBROUTINE ; ------------------------- ; The zx80 character set makes this routine as straightforward as the one above ; as there is no gap between numerals and alphabetic characters. <a name="L0D18"></a>;; <b>ALPHANUM</b> L0D18: CP $1C ; compare to '0' - carry set if less <a name="L0D1A"></a>;; <b>ALPHA-2</b> L0D1A: CCF ; change to carry reset if less. RET NC ; return if less than '0' CP $40 ; compare to character after 'Z' RET ; return with carry set if in the ; range '0' - 'Z' ; ------------------------------------------------ ; THE <b><font color=#333388>'ARITHMETIC OPERATORS AND COMPARISONS'</font></b> TABLE ; ------------------------------------------------ ; This table is indexed with the operator * 2 to access the address of the ; associated routine. <a name="L0D1F"></a>;; <b>TAB-OPS</b> L0D1F: DEFW <A href="#L0D39">L0D39</a> ; $00 subtract DEFW <A href="#L0D3E">L0D3E</a> ; $01 addition DEFW <A href="#L0D44">L0D44</a> ; $02 multiply DEFW <A href="#L0D90">L0D90</a> ; $03 division DEFW <A href="#L0DB5">L0DB5</a> ; $04 and DEFW <A href="#L0DBC">L0DBC</a> ; $05 or DEFW <A href="#L0D70">L0D70</a> ; $06 to-power DEFW <A href="#L0DC3">L0DC3</a> ; $07 nos-eql DEFW <A href="#L0DCC">L0DCC</a> ; $08 no-grtr DEFW <A href="#L0DCD">L0DCD</a> ; $09 no-less DEFW <A href="#L0DD9">L0DD9</a> ; $0A strs-eql DEFW <A href="#L0DDF">L0DDF</a> ; $0B str-grtr DEFW <A href="#L0DDE">L0DDE</a> ; $0C str-less ; --------------------------- ; THE <b><font color=#333388>'SUBTRACTION'</font></b> OPERATION ; --------------------------- ; offset $00 : subtract ; This operation simply uses the Z80's 16-bit register subtract instruction ; which sets the overflow flag if the lower 15 bits overflow. <a name="L0D39"></a>;; <b>subtract</b> L0D39: AND A ; clear carry flag. SBC HL,DE ; 16 bit subtraction. JR <A href="#L0D41">L0D41</a> ; forward to RSLT-TEST ; ------------------------ ; THE <b><font color=#333388>'ADDITION'</font></b> OPERATION ; ------------------------ ; offset $01 : add ; This operation simply uses the Z80's 16-bit register add instruction ; which sets the overflow flag in the manner above. <a name="L0D3E"></a>;; <b>addition</b> L0D3E: AND A ; clear carry flag. ADC HL,DE ; 16 bit addition. <a name="L0D41"></a>;; <b>RSLT-TEST</b> L0D41: RET PO ; return if no twos-complement arithmetic ; overflow. <a name="L0D42"></a>;; <b>ERROR-06</b> L0D42: RST 08H ; ERROR restart DEFB $05 ; arithmetic overflow. ; ------------------------------ ; THE <b><font color=#333388>'MULTIPLICATION'</font></b> OPERATION ; ------------------------------ ; offset $02 : multiply ; the multiplication operation converts the two numbers HL and DE to positive ; integers, saving the result sign in the accumulator. If the positive result ; is above 32767 then an error code is produced else result is converted ; to the required sign, if necessary, as dictated by the accumulator. <a name="L0D44"></a>;; <b>multiply</b> L0D44: CALL <A href="#L0DED">L0DED</a> ; routine PREP-MD PUSH BC ; save priority/operation EX AF,AF' ; save result sign CALL <A href="#L0D55">L0D55</a> ; routine MULT16 JR NZ,<A href="#L0D8D">L0D8D</a> ; forward with overflow to POP6 ; clear the stack and produce ERROR-06 <a name="L0D4E"></a>;; <b>MULT-2</b> L0D4E: POP BC ; restore priority/operation EX AF,AF' ; restore result sign. RRA ; test sign bit. RET NC ; return if result positive. JP <A href="#L0DF6">L0DF6</a> ; exit via routine TWOS-COMP ; ---------------------------------------- ; THE <b><font color=#333388>'SIXTEEN BIT MULTIPLICATION'</font></b> ROUTINE ; ---------------------------------------- ; Binary long multiplication by shifting and addition at the appropriate place ; if the multiplier bit is set. ; This important subroutine is called from the multiply routine, the to-power ; routine and twice from the RND function routine. ; It multiplies the 16 bit multiplier, HL, by the 16-bit multiplicand DE. ; Since the highest number the ZX80 can hold is 32767, the routine detects ; any overflow above this, resetting the zero flag - NZ with overflow. ; However if overflow occurs the routine does not abort, as does say the ; Spectrum, but continues to calculate the 32-bit result in B, C, H, L. ; Use is made of this by the RND routine. <a name="L0D55"></a>;; <b>MULT16</b> L0D55: LD B,H ; transfer HL to BC LD C,L ; register. LD A,$10 ; count 16 bits. LD HL,$0000 ; initialize result register. <a name="L0D5C"></a>;; <b>MULT-LP</b> L0D5C: ADD HL,HL ; shift result left. RL C ; shift multiplier RL B ; to the left. ; and capture any overflow. JR NC,<A href="#L0D67">L0D67</a> ; skip addition if no carry to MULT-SKIP. ADD HL,DE ; else add in multiplicand for this bit JR NC,<A href="#L0D67">L0D67</a> ; forward if no overflow. INC BC ; capture overflow in BC <a name="L0D67"></a>;; <b>MULT-SKIP</b> L0D67: DEC A ; decrement bit count. JR NZ,<A href="#L0D5C">L0D5C</a> ; loop back for all 16 bits to MULT-LP. LD A,H ; test for a AND $80 ; negative result. OR B ; test for any OR C ; intermediate overflow RET ; return with zero flag set ; for success. ; ------------------------ ; THE <b><font color=#333388>'TO-POWER'</font></b> OPERATION ; ------------------------ ; offset $06 : to-power ; This routine raises HL to the power DE, by performing a multiplication ; for each unit of the power. For the integer range supported this is quite ; adequate with 2**14 returning the result without any noticeable delay ; and 1**32767 blacking the screen out for no more than a second. ; Note also that ; 0 ** 0 = 1. ; 0 ** +n = 0. ; 0 ** -n = arithmetic overflow. <a name="L0D70"></a>;; <b>to-power</b> L0D70: BIT 7,D ; test if second number negative. JR NZ,<A href="#L0D42">L0D42</a> ; back to ERROR-06 if so. XOR A ; initialize sign flag CALL <A href="#L0DF2">L0DF2</a> ; routine ABS - makes HL positive. ; A holds 1 if HL was negative else 0. AND E ; EX AF,AF' ; save result PUSH BC ; save priority/operation LD B,D ; transfer power LD C,E ; to BC EX DE,HL ; transfer number to DE LD HL,$0001 ; initialize result. <a name="L0D81"></a>;; <b>POWER-LP</b> L0D81: DEC BC ; decrement power counter. BIT 7,B ; check when zero passed. JR NZ,<A href="#L0D4E">L0D4E</a> ; back when finished to MULT-2 ; to test result. >> PUSH BC ; save counter. CALL <A href="#L0D55">L0D55</a> ; routine MULT16 POP BC ; restore counter. JR Z,<A href="#L0D81">L0D81</a> ; loop while no overflow exists from ; the multiplication to POWER-LP. <a name="L0D8D"></a>;; <b>POP6</b> L0D8D: POP BC ; restore priority/operation JR <A href="#L0D42">L0D42</a> ; back to ERROR-06 - arithmetic overflow. ; ------------------------ ; THE <b><font color=#333388>'DIVISION'</font></b> OPERATION ; ------------------------ ; offset $03 : division ; Binary long division by shifting and subtraction at the appropriate place, ; setting correct quotient bit if the subtraction goes. ; dividend (HL) / divisor (DE) = quotient (HL) <a name="L0D90"></a>;; <b>division</b> L0D90: LD A,D ; test divisor for zero OR E ; avoiding division by zero. JR Z,<A href="#L0D42">L0D42</a> ; to ERROR-06 - arithmetic overflow ; if so. CALL <A href="#L0DED">L0DED</a> ; routine PREP-MD converts HL and DE to 15-bit ; integers and records the result sign in A. PUSH BC ; save the priority/operation. RRA ; sets carry if a negative result. ADC HL,HL ; pick up the carry in HL, (bit 15 was reset) LD A,H ; transfer modified dividend to LD C,L ; registers A and C. LD HL,<A href="#L0000">L0000</a> ; initialize 'accumulator' to zero. LD B,$10 ; sixteen bits including sign bit. <a name="L0DA2"></a>;; <b>DIV-1</b> L0DA2: ADC HL,HL ; SBC HL,DE ; subtract divisor. JR NC,<A href="#L0DA9">L0DA9</a> ; skip forward if subtraction goes to DIV-2. ADD HL,DE ; add back divisor. <a name="L0DA9"></a>;; <b>DIV-2</b> L0DA9: RL C ; as dividend bits are shifted out, the RLA ; result bits are shifted in. DJNZ <A href="#L0DA2">L0DA2</a> ; back for all 16 bits. ; note after 16 bits the final RLA retrieves the sign LD H,A ; transfer result in A and C LD L,C ; to HL INC HL ; increment POP BC ; restore priority/operation. RET C ; return if . JR <A href="#L0DF6">L0DF6</a> ; else forward to TWOS-COMP. ; --------------------------- ; THE <b><font color=#333388>'BITWISE AND'</font></b> OPERATION ; --------------------------- ; offset $04 : and <a name="L0DB5"></a>;; <b>and</b> L0DB5: LD A,H ; AND D ; LD H,A ; LD A,L ; AND E ; LD L,A ; RET ; ; -------------------------- ; THE <b><font color=#333388>'BITWISE OR'</font></b> OPERATION ; -------------------------- ; offset $05 : or <a name="L0DBC"></a>;; <b>or</b> L0DBC: LD A,H ; OR D ; LD H,A ; LD A,L ; OR E ; LD L,A ; RET ; ; ----------------------------------------- ; THE <b><font color=#333388>'THREE NUMERIC COMPARISON'</font></b> OPERATIONS ; ----------------------------------------- ; offsets $07 - nos-eql, $08 - no-grtr, $09 - no-less. ; ; for example, PRINT 2=2 gives result -1 (true) <a name="L0DC3"></a>;; <b>nos-eql</b> L0DC3: AND A ; prepare to subtract. SBC HL,DE ; subtract the two numbers. <a name="L0DC6"></a>;; <b>SET-RSLT</b> L0DC6: LD HL,$FFFF ; prepare true result. RET Z ; return true result, $FFFF, in HL ; if remainder was zero. INC HL ; else increment to $0000 RET ; return false result, zero in HL. ; --- <a name="L0DCC"></a>;; <b>no-grtr</b> L0DCC: EX DE,HL ; swap values and continue into ... <a name="L0DCD"></a>;; <b>no-less</b> L0DCD: AND A ; prepare for true subtraction SBC HL,DE ; subtract using registers LD A,H ; fetch MSB RLA ; test the sign bit without affecting P/V flag JP PO,<A href="#L0DD6">L0DD6</a> ; skip to TEST-HL with no overflow CCF ; complement the carry flag <a name="L0DD6"></a>;; <b>TEST-HL</b> L0DD6: SBC HL,HL ; result HL will be $0000 false or $FFFF true ; with carry. RET ; return ; ---------------------------------------- ; THE <b><font color=#333388>'THREE STRING COMPARISON'</font></b> OPERATIONS ; ---------------------------------------- ; offsets $0A - strs-eql, $0B - str-grtr, $0C - str-less. <a name="L0DD9"></a>;; <b>strs-eql</b> L0DD9: CALL <A href="#L0DE4">L0DE4</a> ; routine STR-CMP JR <A href="#L0DC6">L0DC6</a> ; to SET-RSLT ; --- <a name="L0DDE"></a>;; <b>str-grtr</b> L0DDE: EX DE,HL ; swap the two string pointers <a name="L0DDF"></a>;; <b>str-less</b> L0DDF: CALL <A href="#L0DE4">L0DE4</a> ; routine STR-CMP JR <A href="#L0DD6">L0DD6</a> ; back to TEST-HL ; ---------------------------------- ; THE <b><font color=#333388>'STRING COMPARISON'</font></b> SUBROUTINE ; ---------------------------------- <a name="L0DE4"></a>;; <b>STR-CMP</b> L0DE4: LD A,(DE) ; fetch character of 2nd string. CP (HL) ; compare to first. RET NZ ; return with mismatch, carry flag ; shows the comparison. DEC A ; test for the null string chr$ 1. RET Z ; return as both strings have ; terminated - an exact match. INC DE ; else increase INC HL ; both the string pointers. JR <A href="#L0DE4">L0DE4</a> ; and loop back to STR-CMP till one ; of the two conditions is met. ; ---------------------------------------------- ; THE <b><font color=#333388>'PREPARE TO MULTIPLY OR DIVIDE'</font></b> SUBROUTINE ; ---------------------------------------------- <a name="L0DED"></a>;; <b>PREP-MD</b> L0DED: XOR A ; initialize a sign flag. CALL <A href="#L0DF1">L0DF1</a> ; call PREP-1 to prepare one number ; and continue into routine to prepare ; the other number. <a name="L0DF1"></a>;; <b>PREP-1</b> L0DF1: EX DE,HL ; switch numbers at each pass ; ------------------ ; THE <b><font color=#333388>'ABS'</font></b> FUNCTION ; ------------------ ; finds the absolute value of an signed integer. ; Negative numbers are twos complemented. ; e.g. minus 1 ($FFFF) is first 'ones complemented' to $0000 then incremented. <a name="L0DF2"></a>;; <b>abs</b> L0DF2: BIT 7,H ; test sign of HL. RET Z ; return if positive. INC A ; sets bit 0 if result is negative. ; two negatives will reset bit 0 when this ; routine is used to prepare for multiplication. ; 'a minus times a minus gives a plus'. <a name="L0DF6"></a>;; <b>TWOS-COMP</b> L0DF6: EX AF,AF' ; save running flag. LD A,H ; fetch high byte CPL ; complement it LD H,A ; put back LD A,L ; fetch low byte CPL ; complement LD L,A ; put back INC HL ; twos complement EX AF,AF' ; restore running flag. RET ; return. ; ------------------- ; THE <b><font color=#333388>'SPARE'</font></b> SECTION ; ------------------- ; Start of Spare bytes ; End of Spare bytes. ;-------------------- ; THE <b><font color=#333388>'CHARACTER SET'</font></b> ;-------------------- <a name="L0E00"></a>;; <b>char-set</b> ; $00 - space character CHR$(0) L0E00: DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 ; $01 - <b>Character: '"' </b>CHR$(1) DEFB %00000000 DEFB %000<B>1</B>0<B>1</B>00 DEFB %000<B>1</B>0<B>1</B>00 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 ; $02 - <b>Character: mosaic </b>CHR$(2) DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 ; $03 - <b>Character: mosaic </b>CHR$(3) DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> ; $04 - <b>Character: mosaic </b>CHR$(4) DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 ; $05 - <b>Character: mosaic </b>CHR$(5) DEFB %0000<B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0000<B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0000<B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0000<B>1</B><B>1</B><B>1</B><B>1</B> DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 ; $06 - <b>Character: mosaic </b>CHR$(6) DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 ; $07 - <b>Character: mosaic </b>CHR$(7) DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %0000<B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0000<B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0000<B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0000<B>1</B><B>1</B><B>1</B><B>1</B> ; $08 - <b>Character: mosaic </b>CHR$(8) DEFB %0000<B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0000<B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0000<B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0000<B>1</B><B>1</B><B>1</B><B>1</B> DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 DEFB %<B>1</B><B>1</B><B>1</B><B>1</B>0000 ; $09 - <b>Character: mosaic </b>CHR$(9) DEFB %<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B>0 DEFB %0<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B> DEFB %<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B>0 DEFB %0<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B> DEFB %<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B>0 DEFB %0<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B> DEFB %<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B>0 DEFB %0<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B> ; $0A - <b>Character: mosaic </b>CHR$(10) DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B>0 DEFB %0<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B> DEFB %<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B>0 DEFB %0<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B> ; $0B - <b>Character: mosaic </b>CHR$(11) DEFB %<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B>0 DEFB %0<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B> DEFB %<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B>0 DEFB %0<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B> DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 ; $0C - <b>Character: uk pound </b>CHR$(12) DEFB %00000000 DEFB %000<B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00<B>1</B>0000<B>1</B> DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B>000 DEFB %00<B>1</B>00000 DEFB %00<B>1</B>00000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %00000000 ; $0D - <b>Character: '$' </b>CHR$(13) DEFB %00000000 DEFB %0000<B>1</B>000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00<B>1</B>000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0000<B>1</B>00<B>1</B> DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0000<B>1</B>000 ; $0E - <b>Character: ':' </b>CHR$(14) DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %0000<B>1</B>000 DEFB %00000000 DEFB %00000000 DEFB %0000<B>1</B>000 DEFB %00000000 ; $0F - <b>Character: '?' </b>CHR$(15) DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %00000<B>1</B><B>1</B>0 DEFB %0000<B>1</B>000 DEFB %00000000 DEFB %0000<B>1</B>000 DEFB %00000000 ; $10 - <b>Character: '(' </b>CHR$(16) DEFB %00000000 DEFB %00000<B>1</B>00 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %00000<B>1</B>00 DEFB %00000000 ; $11 - <b>Character: ')' </b>CHR$(17) DEFB %00000000 DEFB %000<B>1</B>0000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %000<B>1</B>0000 DEFB %00000000 ; $12 - <b>Character: '-' </b>CHR$(18) DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 DEFB %00000000 DEFB %00000000 ; $13 - <b>Character: '+' </b>CHR$(19) DEFB %00000000 DEFB %00000000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %00000000 ; $14 - <b>Character: '*' </b>CHR$(20) DEFB %00000000 DEFB %00000000 DEFB %00<B>1</B>0<B>1</B>0<B>1</B>0 DEFB %000<B>1</B><B>1</B><B>1</B>00 DEFB %0000<B>1</B>000 DEFB %000<B>1</B><B>1</B><B>1</B>00 DEFB %00<B>1</B>0<B>1</B>0<B>1</B>0 DEFB %00000000 ; $15 - <b>Character: '/' </b>CHR$(21) DEFB %00000000 DEFB %00000000 DEFB %000000<B>1</B>0 DEFB %00000<B>1</B>00 DEFB %0000<B>1</B>000 DEFB %000<B>1</B>0000 DEFB %00<B>1</B>00000 DEFB %00000000 ; $16 - <b>Character: '=' </b>CHR$(22) DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 DEFB %00000000 ; $17 - <b>Character: '>' </b>CHR$(23) DEFB %00000000 DEFB %00000000 DEFB %000<B>1</B>0000 DEFB %0000<B>1</B>000 DEFB %00000<B>1</B>00 DEFB %0000<B>1</B>000 DEFB %000<B>1</B>0000 DEFB %00000000 ; $18 - <b>Character: '<' </b>CHR$(24) DEFB %00000000 DEFB %00000000 DEFB %00000<B>1</B>00 DEFB %0000<B>1</B>000 DEFB %000<B>1</B>0000 DEFB %0000<B>1</B>000 DEFB %00000<B>1</B>00 DEFB %00000000 ; $19 - <b>Character: ';' </b>CHR$(25) DEFB %00000000 DEFB %00000000 DEFB %0000<B>1</B>000 DEFB %00000000 DEFB %00000000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %000<B>1</B>0000 ; $1A - <b>Character: ',' </b>CHR$(26) DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %000<B>1</B>0000 ; $1B - <b>Character: '.' </b>CHR$(27) DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %00000000 DEFB %0000<B>1</B><B>1</B>00 DEFB %0000<B>1</B><B>1</B>00 DEFB %00000000 ; $1C - <b>Character: '0' </b>CHR$(28) DEFB %00000000 DEFB %000<B>1</B><B>1</B><B>1</B>00 DEFB %00<B>1</B>000<B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00<B>1</B>000<B>1</B>0 DEFB %000<B>1</B><B>1</B><B>1</B>00 DEFB %00000000 ; $1D - <b>Character: '1' </b>CHR$(29) DEFB %00000000 DEFB %0000<B>1</B><B>1</B>00 DEFB %000<B>1</B>0<B>1</B>00 DEFB %00000<B>1</B>00 DEFB %00000<B>1</B>00 DEFB %00000<B>1</B>00 DEFB %000<B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $1E - <b>Character: '2' </b>CHR$(30) DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %0000000<B>1</B> DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %00000000 ; $1F - <b>Character: '3' </b>CHR$(31) DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %00000<B>1</B><B>1</B>0 DEFB %0000000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $20 - <b>Character: '4' </b>CHR$(32) DEFB %00000000 DEFB %0000<B>1</B><B>1</B>00 DEFB %000<B>1</B>0<B>1</B>00 DEFB %00<B>1</B>00<B>1</B>00 DEFB %0<B>1</B>000<B>1</B>00 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %00000<B>1</B>00 DEFB %00000000 ; $21 - <b>Character: '5' </b>CHR$(33) DEFB %00000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0<B>1</B>000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0000000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $22 - <b>Character: '6' </b>CHR$(34) DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $23 - <b>Character: '7' </b>CHR$(35) DEFB %00000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0000000<B>1</B> DEFB %000000<B>1</B>0 DEFB %00000<B>1</B>00 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %00000000 ; $24 - <b>Character: '8' </b>CHR$(36) DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $25 - <b>Character: '9' </b>CHR$(37) DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0000000<B>1</B> DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $26 - <b>Character: 'A' </b>CHR$(38) DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00000000 ; $27 - <b>Character: 'B' </b>CHR$(39) DEFB %00000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $28 - <b>Character: 'C' </b>CHR$(40) DEFB %00000000 DEFB %000<B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00<B>1</B>0000<B>1</B> DEFB %0<B>1</B>000000 DEFB %0<B>1</B>000000 DEFB %00<B>1</B>0000<B>1</B> DEFB %000<B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $29 - <b>Character: 'D' </b>CHR$(41) DEFB %00000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>00 DEFB %0<B>1</B>0000<B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>0000<B>1</B>0 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>00 DEFB %00000000 ; $2A - <b>Character: 'E' </b>CHR$(42) DEFB %00000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0<B>1</B>000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>00 DEFB %0<B>1</B>000000 DEFB %0<B>1</B>000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %00000000 ; $2B - <b>Character: 'F' </b>CHR$(43) DEFB %00000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0<B>1</B>000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>00 DEFB %0<B>1</B>000000 DEFB %0<B>1</B>000000 DEFB %0<B>1</B>000000 DEFB %00000000 ; $2C - <b>Character: 'G' </b>CHR$(44) DEFB %00000000 DEFB %000<B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00<B>1</B>0000<B>1</B> DEFB %0<B>1</B>000000 DEFB %0<B>1</B>000<B>1</B><B>1</B><B>1</B> DEFB %00<B>1</B>0000<B>1</B> DEFB %000<B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $2D - <b>Character: 'H' </b>CHR$(45) DEFB %00000000 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00000000 ; $2E - <b>Character: 'I' </b>CHR$(46) DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $2F - <b>Character: 'J' </b>CHR$(47) DEFB %00000000 DEFB %000000<B>1</B>0 DEFB %000000<B>1</B>0 DEFB %000000<B>1</B>0 DEFB %0<B>1</B>0000<B>1</B>0 DEFB %00<B>1</B>000<B>1</B>0 DEFB %000<B>1</B><B>1</B><B>1</B>00 DEFB %00000000 ; $30 - <b>Character: 'K' </b>CHR$(48) DEFB %00000000 DEFB %0<B>1</B>0000<B>1</B>0 DEFB %0<B>1</B>000<B>1</B>00 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B>000 DEFB %0<B>1</B>000<B>1</B>00 DEFB %0<B>1</B>0000<B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %00000000 ; $31 - <b>Character: 'L' </b>CHR$(49) DEFB %00000000 DEFB %0<B>1</B>000000 DEFB %0<B>1</B>000000 DEFB %0<B>1</B>000000 DEFB %0<B>1</B>000000 DEFB %0<B>1</B>000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %00000000 ; $32 - <b>Character: 'M' </b>CHR$(50) DEFB %00000000 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B><B>1</B>000<B>1</B><B>1</B> DEFB %0<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B> DEFB %0<B>1</B>00<B>1</B>00<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00000000 ; $33 - <b>Character: 'N' </b>CHR$(51) DEFB %00000000 DEFB %0<B>1</B><B>1</B>0000<B>1</B> DEFB %0<B>1</B>0<B>1</B>000<B>1</B> DEFB %0<B>1</B>00<B>1</B>00<B>1</B> DEFB %0<B>1</B>000<B>1</B>0<B>1</B> DEFB %0<B>1</B>0000<B>1</B><B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00000000 ; $34 - <b>Character: 'O' </b>CHR$(52) DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $35 - <b>Character: 'P' </b>CHR$(53) DEFB %00000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>000000 DEFB %0<B>1</B>000000 DEFB %00000000 ; $36 - <b>Character: 'Q' </b>CHR$(54) DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00<B>1</B>00<B>1</B> DEFB %0<B>1</B>000<B>1</B>0<B>1</B> DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $37 - <b>Character: 'R' </b>CHR$(55) DEFB %00000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>000<B>1</B>00 DEFB %0<B>1</B>0000<B>1</B>0 DEFB %00000000 ; $38 - <b>Character: 'S' </b>CHR$(56) DEFB %00000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0<B>1</B>000000 DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %0000000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $39 - <b>Character: 'T' </b>CHR$(57) DEFB %00000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %00000000 ; $3A - <b>Character: 'U' </b>CHR$(58) DEFB %00000000 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B>0 DEFB %00000000 ; $3B - <b>Character: 'V' </b>CHR$(59) DEFB %00000000 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %00<B>1</B>000<B>1</B>0 DEFB %000<B>1</B>0<B>1</B>00 DEFB %0000<B>1</B>000 DEFB %00000000 ; $3C - <b>Character: 'W' </b>CHR$(60) DEFB %00000000 DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00000<B>1</B> DEFB %0<B>1</B>00<B>1</B>00<B>1</B> DEFB %0<B>1</B>0<B>1</B>0<B>1</B>0<B>1</B> DEFB %00<B>1</B>000<B>1</B>0 DEFB %00000000 ; $3D - <b>Character: 'X' </b>CHR$(61) DEFB %00000000 DEFB %00<B>1</B>0000<B>1</B> DEFB %000<B>1</B>00<B>1</B>0 DEFB %0000<B>1</B><B>1</B>00 DEFB %0000<B>1</B><B>1</B>00 DEFB %000<B>1</B>00<B>1</B>0 DEFB %00<B>1</B>0000<B>1</B> DEFB %00000000 ; $3E - <b>Character: 'Y' </b>CHR$(62) DEFB %00000000 DEFB %0<B>1</B>00000<B>1</B> DEFB %00<B>1</B>000<B>1</B>0 DEFB %000<B>1</B><B>1</B><B>1</B>00 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %0000<B>1</B>000 DEFB %00000000 ; $3F - <b>Character: 'Z' </b>CHR$(63) DEFB %00000000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> DEFB %000000<B>1</B>0 DEFB %00000<B>1</B>00 DEFB %0000<B>1</B>000 DEFB %000<B>1</B>0000 DEFB %0<B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B><B>1</B> L0FFF: DEFB %00000000 .END ;TASM assembler directive. ; ----------------------------------------------------------------------------- ; ; ------------------- ; The <b><font color=#333388>'Character set'</font></b> ; ------------------- ; ; $00 $01 $02 $03 $04 $05 $06 $07 $08 $09 $0A $0B $0C $0D $0E $0F ; nul gra gra gra gra gra gra gra gra gra gra £ $ : ? ; ; $10 $11 $12 $13 $14 $15 $16 $17 $18 $19 $1A $1B $1C $1D $1E $1F ; ( ) - + * / = > < ; , . 0 1 2 3 ; ; $20 $21 $22 $23 $24 $25 $26 $27 $28 $29 $2A $2B $2C $2D $2E $2F ; 4 5 6 7 8 9 A B C D E F G H I J ; ; $30 $31 $32 $33 $34 $35 $36 $37 $38 $39 $3A $3B $3C $3D $3E $3F ; K L M N O P Q R S T U V W X Y Z ; ; ----------------------------------------------------------------------------- ; ; ------------------- ; THE <b><font color=#333388>'ZX80 KEYBOARD'</font></b> ; ------------------- ; [] mosaic graphic £ currency symbol ; ; NOT AND THEN TO <= V ^ => HOME RUBOUT ;+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ ;| | | | | | | | | | | | | | | | | | | | ;| 1 | | 2 | | 3 | | 4 | | 5 | | 6 | | 7 | | 8 | | 9 | | 0 | ;+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ ; ; NEW LOAD SAVE RUN CONT REM IF INPUT PRINT ;+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ ;| [] | | [] | | [] | | [] | | [] | | " | | $ | | ( | | ) | | * | ;| Q | | W | | E | | R | | T | | Y | | U | | I | | O | | P | ;+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ ; ; LIST STOP DIM FOR GOTO POKE RAND LET EDIT ;+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ ;| [] | | [] | | [] | | [] | | [] | | ** | | - | | + | | = | | NEW | ;| A | | S | | D | | F | | G | | H | | J | | K | | L | | LINE| ;+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ ; ; CLEAR CLS GOSUB RET NEXT BREAK ;+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ ;| | | : | | ; | | ? | | / | | OR | | < | | > | | , | | £ | ;|SHIFT| | Z | | X | | C | | V | | B | | N | | M | | . | |SPACE| ;+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ ; ; ; ; ----------------------------------------------------------------------------- ; ; ---------------------- ; THE <b><font color=#333388>'SYSTEM VARIABLES'</font></b> ; ---------------------- ; <font color=#9900FF>Note.</font> the names of the System Variables are taken from the original ; Nine Tiles Assembly Listing. ; ; 1 16384 $4000 IY+$00 ERR_NR One less than report code. ; X1 16385 $4001 IY+$01 FLAGS Various Flags to control BASIC System. ; 7 1-Syntax off 0-Syntax on ; 6 1-Numeric result 0-String result ; 5 1-Evaluating function (not used) ; 3 1-K cursor 0-L cursor ; 2 1-K mode 0-L mode. ; 0 1-No leading space 0-Leading space. ; 2 16386 $4002 IY+$02 PPC Line number of current line. ; N2 16388 $4004 IY+$04 P_PTR. Position in RAM of [K] or [L] cursor. ; 2 16390 $4006 IY+$06 E_PPC Number of current line with [>] cursor. ; X2 16392 $4008 IY+$08 VARS Address of start of variables area. ; X2 16394 $400A IY+$0A E_LINE Address of start of Edit Line. ; X2 16396 $400C IY+$0C D_FILE Start of Display File. ; X2 16398 $400E IY+$0E DF_EA Address of the start of lower screen. ; X2 16400 $4010 IY+$10 DF_END Display File End. ; X1 16402 $4012 IY+$12 DF_SZ Number of lines in lower screen. ; 2 16403 $4013 IY+$13 S_TOP. The number of first line on screen. ; 2 16405 $4015 IY+$15 X_PTR Address of the character preceding ; the [S] marker. ; 2 16407 $4017 IY+$17 OLDPPC Line number to which continue jumps. ; N1 16409 $4019 IY+$19 FLAGX. More flags. ; 7 1-K mode 0-L mode. ; 6 1-Numeric result 0-String result ; 5 1-Inputting 0-Editing ; N2 16410 $401A IY+$1A T_ADDR Address of next item in syntax table. ; U2 16412 $401C IY+$1C SEED The seed for the random number. ; U2 16414 $401E IY+$1E FRAMES Count of frames shown since start-up. ; N2 16416 $4020 IY+$20 DEST Address of variable in statement. ; N2 16418 $4022 IY+$22 RESULT. Value of the last expression. ; X1 16420 $4024 IY+$24 S_POSN_X Column number for print position. ; X1 16421 $4025 IY+$25 S_POSN_Y Line number for print position. ; X2 16422 $4026 IY+$26 CH_ADD. Address of next character to be ; interpreted. ; ; -----------------------------------------------------------------------------
assembly_listing_of_the_operating_system_of_the_sinclair_zx80.1647864767.txt.gz ยท Last modified: 2022/03/21 12:12 by evert