; Prog8 definitions for the Commodore-64 ; These are the utility subroutines. ; ; Written by Irmen de Jong (irmen@razorvine.net) - license: GNU GPL 3.0 ; ; indent format: TABS, size=8 %import c64lib c64utils { const uword ESTACK_LO = $ce00 const uword ESTACK_HI = $cf00 ; ----- utility functions ---- asmsub ubyte2decimal (ubyte value @ A) -> ubyte @ Y, ubyte @ X, ubyte @ A { ; ---- A to decimal string in Y/X/A (100s in Y, 10s in X, 1s in A) %asm {{ ldy #$2f ldx #$3a sec - iny sbc #100 bcs - - dex adc #10 bmi - adc #$2f rts }} } asmsub byte2decimal (ubyte value @ A) -> ubyte @ Y, ubyte @ X, ubyte @ A { ; ---- A (signed byte) to decimal string in Y/X/A (100s in Y, 10s in X, 1s in A) ; note: the '-' is not part of the conversion here if it's a negative number %asm {{ cmp #0 bpl + eor #255 clc adc #1 + jmp ubyte2decimal }} } asmsub ubyte2hex (ubyte value @ A) -> ubyte @ A, ubyte @ Y { ; ---- A to hex string in AY (first hex char in A, second hex char in Y) %asm {{ stx c64.SCRATCH_ZPREGX pha and #$0f tax ldy _hex_digits,x pla lsr a lsr a lsr a lsr a tax lda _hex_digits,x ldx c64.SCRATCH_ZPREGX rts _hex_digits .text "0123456789abcdef" ; can probably be reused for other stuff as well }} } asmsub uword2hex (uword value @ AY) clobbers(A,Y) { ; ---- convert 16 bit uword in A/Y into 4-character hexadecimal string 'uword2hex.output' (0-terminated) %asm {{ sta c64.SCRATCH_ZPREG tya jsr ubyte2hex sta output sty output+1 lda c64.SCRATCH_ZPREG jsr ubyte2hex sta output+2 sty output+3 rts output .text "0000", $00 ; 0-terminated output buffer (to make printing easier) }} } asmsub uword2bcd (uword value @ AY) clobbers(A,Y) { ; Convert an 16 bit binary value to BCD ; ; This function converts a 16 bit binary value in A/Y into a 24 bit BCD. It ; works by transferring one bit a time from the source and adding it ; into a BCD value that is being doubled on each iteration. As all the ; arithmetic is being done in BCD the result is a binary to decimal ; conversion. %asm {{ sta c64.SCRATCH_ZPB1 sty c64.SCRATCH_ZPREG php pla ; read status register and #%00000100 sta _had_irqd sei ; disable interrupts because of bcd math sed ; switch to decimal mode lda #0 ; ensure the result is clear sta bcdbuff+0 sta bcdbuff+1 sta bcdbuff+2 ldy #16 ; the number of source bits - asl c64.SCRATCH_ZPB1 ; shift out one bit rol c64.SCRATCH_ZPREG lda bcdbuff+0 ; and add into result adc bcdbuff+0 sta bcdbuff+0 lda bcdbuff+1 ; propagating any carry adc bcdbuff+1 sta bcdbuff+1 lda bcdbuff+2 ; ... thru whole result adc bcdbuff+2 sta bcdbuff+2 dey ; and repeat for next bit bne - cld ; back to binary lda _had_irqd bne + cli ; enable interrupts again (only if they were enabled before) + rts _had_irqd .byte 0 bcdbuff .byte 0,0,0 }} } asmsub uword2decimal (uword value @ AY) clobbers(A) -> ubyte @ Y { ; ---- convert 16 bit uword in A/Y into 0-terminated decimal string into memory 'uword2decimal.output' ; returns length of resulting string in Y %asm {{ jsr uword2bcd lda uword2bcd.bcdbuff+2 clc adc #'0' sta output ldy #1 lda uword2bcd.bcdbuff+1 jsr + lda uword2bcd.bcdbuff+0 + pha lsr a lsr a lsr a lsr a clc adc #'0' sta output,y iny pla and #$0f adc #'0' sta output,y iny lda #0 sta output,y rts output .text "00000", $00 ; 0 terminated }} } asmsub str2uword(str string @ AY) -> uword @ AY { ; -- returns the unsigned word value of the string number argument in AY ; the number may NOT be preceded by a + sign and may NOT contain spaces ; (any non-digit character will terminate the number string that is parsed) %asm {{ _result = c64.SCRATCH_ZPWORD2 sta _mod+1 sty _mod+2 ldy #0 sty _result sty _result+1 _mod lda $ffff,y ; modified sec sbc #48 bpl + _done ; return result lda _result ldy _result+1 rts + cmp #10 bcs _done ; add digit to result pha jsr _result_times_10 pla clc adc _result sta _result bcc + inc _result+1 + iny bne _mod ; never reached _result_times_10 ; (W*4 + W)*2 lda _result+1 sta c64.SCRATCH_ZPREG lda _result asl a rol c64.SCRATCH_ZPREG asl a rol c64.SCRATCH_ZPREG clc adc _result sta _result lda c64.SCRATCH_ZPREG adc _result+1 asl _result rol a sta _result+1 rts }} } asmsub str2word(str string @ AY) -> word @ AY { ; -- returns the signed word value of the string number argument in AY ; the number may be preceded by a + or - sign but may NOT contain spaces ; (any non-digit character will terminate the number string that is parsed) %asm {{ _result = c64.SCRATCH_ZPWORD2 sta c64.SCRATCH_ZPWORD1 sty c64.SCRATCH_ZPWORD1+1 ldy #0 sty _result sty _result+1 sty _negative lda (c64.SCRATCH_ZPWORD1),y cmp #'+' bne + iny + cmp #'-' bne _parse inc _negative iny _parse lda (c64.SCRATCH_ZPWORD1),y sec sbc #48 bpl _digit _done ; return result lda _negative beq + sec lda #0 sbc _result sta _result lda #0 sbc _result+1 sta _result+1 + lda _result ldy _result+1 rts _digit cmp #10 bcs _done ; add digit to result pha jsr str2uword._result_times_10 pla clc adc _result sta _result bcc + inc _result+1 + iny bne _parse ; never reached _negative .byte 0 }} } asmsub set_irqvec_excl() clobbers(A) { %asm {{ sei lda #<_irq_handler sta c64.CINV lda #>_irq_handler sta c64.CINV+1 cli rts _irq_handler jsr set_irqvec._irq_handler_init jsr irq.irq jsr set_irqvec._irq_handler_end lda #$ff sta c64.VICIRQ ; acknowledge raster irq lda c64.CIA1ICR ; acknowledge CIA1 interrupt jmp c64.IRQDFEND ; end irq processing - don't call kernel }} } asmsub set_irqvec() clobbers(A) { %asm {{ sei lda #<_irq_handler sta c64.CINV lda #>_irq_handler sta c64.CINV+1 cli rts _irq_handler jsr _irq_handler_init jsr irq.irq jsr _irq_handler_end jmp c64.IRQDFRT ; continue with normal kernel irq routine _irq_handler_init ; save all zp scratch registers and the X register as these might be clobbered by the irq routine stx IRQ_X_REG lda c64.SCRATCH_ZPB1 sta IRQ_SCRATCH_ZPB1 lda c64.SCRATCH_ZPREG sta IRQ_SCRATCH_ZPREG lda c64.SCRATCH_ZPREGX sta IRQ_SCRATCH_ZPREGX lda c64.SCRATCH_ZPWORD1 sta IRQ_SCRATCH_ZPWORD1 lda c64.SCRATCH_ZPWORD1+1 sta IRQ_SCRATCH_ZPWORD1+1 lda c64.SCRATCH_ZPWORD2 sta IRQ_SCRATCH_ZPWORD2 lda c64.SCRATCH_ZPWORD2+1 sta IRQ_SCRATCH_ZPWORD2+1 ; stack protector; make sure we don't clobber the top of the evaluation stack dex dex dex dex dex dex rts _irq_handler_end ; restore all zp scratch registers and the X register lda IRQ_SCRATCH_ZPB1 sta c64.SCRATCH_ZPB1 lda IRQ_SCRATCH_ZPREG sta c64.SCRATCH_ZPREG lda IRQ_SCRATCH_ZPREGX sta c64.SCRATCH_ZPREGX lda IRQ_SCRATCH_ZPWORD1 sta c64.SCRATCH_ZPWORD1 lda IRQ_SCRATCH_ZPWORD1+1 sta c64.SCRATCH_ZPWORD1+1 lda IRQ_SCRATCH_ZPWORD2 sta c64.SCRATCH_ZPWORD2 lda IRQ_SCRATCH_ZPWORD2+1 sta c64.SCRATCH_ZPWORD2+1 ldx IRQ_X_REG rts IRQ_X_REG .byte 0 IRQ_SCRATCH_ZPB1 .byte 0 IRQ_SCRATCH_ZPREG .byte 0 IRQ_SCRATCH_ZPREGX .byte 0 IRQ_SCRATCH_ZPWORD1 .word 0 IRQ_SCRATCH_ZPWORD2 .word 0 }} } asmsub restore_irqvec() { %asm {{ sei lda #c64.IRQDFRT sta c64.CINV+1 lda #0 sta c64.IREQMASK ; disable raster irq lda #%10000001 sta c64.CIA1ICR ; restore CIA1 irq cli rts }} } asmsub set_rasterirq(uword rasterpos @ AY) clobbers(A) { %asm {{ sei jsr _setup_raster_irq lda #<_raster_irq_handler sta c64.CINV lda #>_raster_irq_handler sta c64.CINV+1 cli rts _raster_irq_handler jsr set_irqvec._irq_handler_init jsr irq.irq jsr set_irqvec._irq_handler_end lda #$ff sta c64.VICIRQ ; acknowledge raster irq jmp c64.IRQDFRT _setup_raster_irq pha lda #%01111111 sta c64.CIA1ICR ; "switch off" interrupts signals from cia-1 sta c64.CIA2ICR ; "switch off" interrupts signals from cia-2 and c64.SCROLY sta c64.SCROLY ; clear most significant bit of raster position lda c64.CIA1ICR ; ack previous irq lda c64.CIA2ICR ; ack previous irq pla sta c64.RASTER ; set the raster line number where interrupt should occur cpy #0 beq + lda c64.SCROLY ora #%10000000 sta c64.SCROLY ; set most significant bit of raster position + lda #%00000001 sta c64.IREQMASK ;enable raster interrupt signals from vic rts }} } asmsub set_rasterirq_excl(uword rasterpos @ AY) clobbers(A) { %asm {{ sei jsr set_rasterirq._setup_raster_irq lda #<_raster_irq_handler sta c64.CINV lda #>_raster_irq_handler sta c64.CINV+1 cli rts _raster_irq_handler jsr set_irqvec._irq_handler_init jsr irq.irq jsr set_irqvec._irq_handler_end lda #$ff sta c64.VICIRQ ; acknowledge raster irq jmp c64.IRQDFEND ; end irq processing - don't call kernel }} } } ; ------ end of block c64utils c64scr { ; ---- this block contains (character) Screen and text I/O related functions ---- asmsub clear_screen (ubyte char @ A, ubyte color @ Y) clobbers(A) { ; ---- clear the character screen with the given fill character and character color. ; (assumes screen and color matrix are at their default addresses) %asm {{ pha tya jsr clear_screencolors pla jsr clear_screenchars rts }} } asmsub clear_screenchars (ubyte char @ A) clobbers(Y) { ; ---- clear the character screen with the given fill character (leaves colors) ; (assumes screen matrix is at the default address) %asm {{ ldy #0 _loop sta c64.Screen,y sta c64.Screen+1,y sta c64.Screen+$0100,y sta c64.Screen+$0101,y sta c64.Screen+$0200,y sta c64.Screen+$0201,y sta c64.Screen+$02e8,y sta c64.Screen+$02e9,y iny iny bne _loop rts }} } asmsub clear_screencolors (ubyte color @ A) clobbers(Y) { ; ---- clear the character screen colors with the given color (leaves characters). ; (assumes color matrix is at the default address) %asm {{ ldy #0 _loop sta c64.Colors,y sta c64.Colors+1,y sta c64.Colors+$0100,y sta c64.Colors+$0101,y sta c64.Colors+$0200,y sta c64.Colors+$0201,y sta c64.Colors+$02e8,y sta c64.Colors+$02e9,y iny iny bne _loop rts }} } asmsub scroll_left_full (ubyte alsocolors @ Pc) clobbers(A, Y) { ; ---- scroll the whole screen 1 character to the left ; contents of the rightmost column are unchanged, you should clear/refill this yourself ; Carry flag determines if screen color data must be scrolled too %asm {{ stx c64.SCRATCH_ZPREGX bcs + jmp _scroll_screen + ; scroll the color memory ldx #0 ldy #38 - .for row=0, row<=12, row+=1 lda c64.Colors + 40*row + 1,x sta c64.Colors + 40*row,x .next inx dey bpl - ldx #0 ldy #38 - .for row=13, row<=24, row+=1 lda c64.Colors + 40*row + 1,x sta c64.Colors + 40*row,x .next inx dey bpl - _scroll_screen ; scroll the screen memory ldx #0 ldy #38 - .for row=0, row<=12, row+=1 lda c64.Screen + 40*row + 1,x sta c64.Screen + 40*row,x .next inx dey bpl - ldx #0 ldy #38 - .for row=13, row<=24, row+=1 lda c64.Screen + 40*row + 1,x sta c64.Screen + 40*row,x .next inx dey bpl - ldx c64.SCRATCH_ZPREGX rts }} } asmsub scroll_right_full (ubyte alsocolors @ Pc) clobbers(A) { ; ---- scroll the whole screen 1 character to the right ; contents of the leftmost column are unchanged, you should clear/refill this yourself ; Carry flag determines if screen color data must be scrolled too %asm {{ stx c64.SCRATCH_ZPREGX bcs + jmp _scroll_screen + ; scroll the color memory ldx #38 - .for row=0, row<=12, row+=1 lda c64.Colors + 40*row + 0,x sta c64.Colors + 40*row + 1,x .next dex bpl - ldx #38 - .for row=13, row<=24, row+=1 lda c64.Colors + 40*row,x sta c64.Colors + 40*row + 1,x .next dex bpl - _scroll_screen ; scroll the screen memory ldx #38 - .for row=0, row<=12, row+=1 lda c64.Screen + 40*row + 0,x sta c64.Screen + 40*row + 1,x .next dex bpl - ldx #38 - .for row=13, row<=24, row+=1 lda c64.Screen + 40*row,x sta c64.Screen + 40*row + 1,x .next dex bpl - ldx c64.SCRATCH_ZPREGX rts }} } asmsub scroll_up_full (ubyte alsocolors @ Pc) clobbers(A) { ; ---- scroll the whole screen 1 character up ; contents of the bottom row are unchanged, you should refill/clear this yourself ; Carry flag determines if screen color data must be scrolled too %asm {{ stx c64.SCRATCH_ZPREGX bcs + jmp _scroll_screen + ; scroll the color memory ldx #39 - .for row=1, row<=11, row+=1 lda c64.Colors + 40*row,x sta c64.Colors + 40*(row-1),x .next dex bpl - ldx #39 - .for row=12, row<=24, row+=1 lda c64.Colors + 40*row,x sta c64.Colors + 40*(row-1),x .next dex bpl - _scroll_screen ; scroll the screen memory ldx #39 - .for row=1, row<=11, row+=1 lda c64.Screen + 40*row,x sta c64.Screen + 40*(row-1),x .next dex bpl - ldx #39 - .for row=12, row<=24, row+=1 lda c64.Screen + 40*row,x sta c64.Screen + 40*(row-1),x .next dex bpl - ldx c64.SCRATCH_ZPREGX rts }} } asmsub scroll_down_full (ubyte alsocolors @ Pc) clobbers(A) { ; ---- scroll the whole screen 1 character down ; contents of the top row are unchanged, you should refill/clear this yourself ; Carry flag determines if screen color data must be scrolled too %asm {{ stx c64.SCRATCH_ZPREGX bcs + jmp _scroll_screen + ; scroll the color memory ldx #39 - .for row=23, row>=12, row-=1 lda c64.Colors + 40*row,x sta c64.Colors + 40*(row+1),x .next dex bpl - ldx #39 - .for row=11, row>=0, row-=1 lda c64.Colors + 40*row,x sta c64.Colors + 40*(row+1),x .next dex bpl - _scroll_screen ; scroll the screen memory ldx #39 - .for row=23, row>=12, row-=1 lda c64.Screen + 40*row,x sta c64.Screen + 40*(row+1),x .next dex bpl - ldx #39 - .for row=11, row>=0, row-=1 lda c64.Screen + 40*row,x sta c64.Screen + 40*(row+1),x .next dex bpl - ldx c64.SCRATCH_ZPREGX rts }} } asmsub print (str text @ AY) clobbers(A,Y) { ; ---- print null terminated string from A/Y ; note: the compiler contains an optimization that will replace ; a call to this subroutine with a string argument of just one char, ; by just one call to c64.CHROUT of that single char. %asm {{ sta c64.SCRATCH_ZPB1 sty c64.SCRATCH_ZPREG ldy #0 - lda (c64.SCRATCH_ZPB1),y beq + jsr c64.CHROUT iny bne - + rts }} } asmsub print_ub0 (ubyte value @ A) clobbers(A,Y) { ; ---- print the ubyte in A in decimal form, with left padding 0s (3 positions total) %asm {{ stx c64.SCRATCH_ZPREGX jsr c64utils.ubyte2decimal pha tya jsr c64.CHROUT txa jsr c64.CHROUT pla jsr c64.CHROUT ldx c64.SCRATCH_ZPREGX rts }} } asmsub print_ub (ubyte value @ A) clobbers(A,Y) { ; ---- print the ubyte in A in decimal form, without left padding 0s %asm {{ stx c64.SCRATCH_ZPREGX jsr c64utils.ubyte2decimal _print_byte_digits pha cpy #'0' bne _print_hundreds cpx #'0' bne _print_tens jmp _end _print_hundreds tya jsr c64.CHROUT _print_tens txa jsr c64.CHROUT _end pla jsr c64.CHROUT ldx c64.SCRATCH_ZPREGX rts }} } asmsub print_b (byte value @ A) clobbers(A,Y) { ; ---- print the byte in A in decimal form, without left padding 0s %asm {{ stx c64.SCRATCH_ZPREGX pha cmp #0 bpl + lda #'-' jsr c64.CHROUT + pla jsr c64utils.byte2decimal jsr print_ub._print_byte_digits ldx c64.SCRATCH_ZPREGX rts }} } asmsub print_ubhex (ubyte value @ A, ubyte prefix @ Pc) clobbers(A,Y) { ; ---- print the ubyte in A in hex form (if Carry is set, a radix prefix '$' is printed as well) %asm {{ stx c64.SCRATCH_ZPREGX bcc + pha lda #'$' jsr c64.CHROUT pla + jsr c64utils.ubyte2hex jsr c64.CHROUT tya jsr c64.CHROUT ldx c64.SCRATCH_ZPREGX rts }} } asmsub print_ubbin (ubyte value @ A, ubyte prefix @ Pc) clobbers(A,Y) { ; ---- print the ubyte in A in binary form (if Carry is set, a radix prefix '%' is printed as well) %asm {{ stx c64.SCRATCH_ZPREGX sta c64.SCRATCH_ZPB1 bcc + lda #'%' jsr c64.CHROUT + ldy #8 - lda #'0' asl c64.SCRATCH_ZPB1 bcc + lda #'1' + jsr c64.CHROUT dey bne - ldx c64.SCRATCH_ZPREGX rts }} } asmsub print_uwbin (uword value @ AY, ubyte prefix @ Pc) clobbers(A,Y) { ; ---- print the uword in A/Y in binary form (if Carry is set, a radix prefix '%' is printed as well) %asm {{ pha tya jsr print_ubbin pla clc jmp print_ubbin }} } asmsub print_uwhex (uword value @ AY, ubyte prefix @ Pc) clobbers(A,Y) { ; ---- print the uword in A/Y in hexadecimal form (4 digits) ; (if Carry is set, a radix prefix '$' is printed as well) %asm {{ pha tya jsr print_ubhex pla clc jmp print_ubhex }} } asmsub print_uw0 (uword value @ AY) clobbers(A,Y) { ; ---- print the uword in A/Y in decimal form, with left padding 0s (5 positions total) %asm {{ jsr c64utils.uword2decimal ldy #0 - lda c64utils.uword2decimal.output,y jsr c64.CHROUT iny cpy #5 bne - rts }} } asmsub print_uw (uword value @ AY) clobbers(A,Y) { ; ---- print the uword in A/Y in decimal form, without left padding 0s %asm {{ jsr c64utils.uword2decimal ldy #0 lda c64utils.uword2decimal.output cmp #'0' bne _pr_decimal iny lda c64utils.uword2decimal.output+1 cmp #'0' bne _pr_decimal iny lda c64utils.uword2decimal.output+2 cmp #'0' bne _pr_decimal iny lda c64utils.uword2decimal.output+3 cmp #'0' bne _pr_decimal iny _pr_decimal lda c64utils.uword2decimal.output,y jsr c64.CHROUT iny cpy #5 bcc _pr_decimal rts }} } asmsub print_w (word value @ AY) clobbers(A,Y) { ; ---- print the (signed) word in A/Y in decimal form, without left padding 0's %asm {{ cpy #0 bpl + pha lda #'-' jsr c64.CHROUT tya eor #255 tay pla eor #255 clc adc #1 bcc + iny + jmp print_uw }} } asmsub input_chars (uword buffer @ AY) clobbers(A) -> ubyte @ Y { ; ---- Input a string (max. 80 chars) from the keyboard. Returns length in Y. (string is terminated with a 0 byte as well) ; It assumes the keyboard is selected as I/O channel! %asm {{ sta c64.SCRATCH_ZPWORD1 sty c64.SCRATCH_ZPWORD1+1 ldy #0 ; char counter = 0 - jsr c64.CHRIN cmp #$0d ; return (ascii 13) pressed? beq + ; yes, end. sta (c64.SCRATCH_ZPWORD1),y ; else store char in buffer iny bne - + lda #0 sta (c64.SCRATCH_ZPWORD1),y ; finish string with 0 byte rts }} } asmsub setchr (ubyte col @Y, ubyte row @A) clobbers(A) { ; ---- set the character in SCRATCH_ZPB1 on the screen matrix at the given position %asm {{ sty c64.SCRATCH_ZPREG asl a tay lda _screenrows+1,y sta _mod+2 lda _screenrows,y clc adc c64.SCRATCH_ZPREG sta _mod+1 bcc + inc _mod+2 + lda c64.SCRATCH_ZPB1 _mod sta $ffff ; modified rts _screenrows .word $0400 + range(0, 1000, 40) }} } asmsub getchr (ubyte col @Y, ubyte row @A) clobbers(Y) -> ubyte @ A { ; ---- get the character in the screen matrix at the given location %asm {{ sty c64.SCRATCH_ZPB1 asl a tay lda setchr._screenrows+1,y sta _mod+2 lda setchr._screenrows,y clc adc c64.SCRATCH_ZPB1 sta _mod+1 bcc _mod inc _mod+2 _mod lda $ffff ; modified rts }} } asmsub setclr (ubyte col @Y, ubyte row @A) clobbers(A) { ; ---- set the color in SCRATCH_ZPB1 on the screen matrix at the given position %asm {{ sty c64.SCRATCH_ZPREG asl a tay lda _colorrows+1,y sta _mod+2 lda _colorrows,y clc adc c64.SCRATCH_ZPREG sta _mod+1 bcc + inc _mod+2 + lda c64.SCRATCH_ZPB1 _mod sta $ffff ; modified rts _colorrows .word $d800 + range(0, 1000, 40) }} } asmsub getclr (ubyte col @Y, ubyte row @A) clobbers(Y) -> ubyte @ A { ; ---- get the color in the screen color matrix at the given location %asm {{ sty c64.SCRATCH_ZPB1 asl a tay lda setclr._colorrows+1,y sta _mod+2 lda setclr._colorrows,y clc adc c64.SCRATCH_ZPB1 sta _mod+1 bcc _mod inc _mod+2 _mod lda $ffff ; modified rts }} } sub setcc (ubyte column, ubyte row, ubyte char, ubyte color) { ; ---- set char+color at the given position on the screen %asm {{ lda row asl a tay lda setchr._screenrows+1,y sta _charmod+2 adc #$d4 sta _colormod+2 lda setchr._screenrows,y clc adc column sta _charmod+1 sta _colormod+1 bcc + inc _charmod+2 inc _colormod+2 + lda char _charmod sta $ffff ; modified lda color _colormod sta $ffff ; modified rts }} } asmsub plot (ubyte col @ Y, ubyte row @ A) clobbers(A) { ; ---- safe wrapper around PLOT kernel routine, to save the X register. %asm {{ stx c64.SCRATCH_ZPREGX tax clc jsr c64.PLOT ldx c64.SCRATCH_ZPREGX rts }} } } ; ---- end block c64scr