Difference between revisions of "6502 Emulator Example Code"
Chris Tyler (talk | contribs) (→Type on the Screen) |
Chris Tyler (talk | contribs) (→Place a Graphic on the Screen) |
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define WIDTH 4 ; width of graphic | define WIDTH 4 ; width of graphic | ||
define HEIGHT 4 ; height of graphic | define HEIGHT 4 ; height of graphic | ||
| − | + | ||
| − | + | ||
lda #$25 ; create a pointer at $10 | lda #$25 ; create a pointer at $10 | ||
sta $10 ; which points to where | sta $10 ; which points to where | ||
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iny | iny | ||
cpy #WIDTH | cpy #WIDTH | ||
| − | + | bne draw | |
| − | + | ||
inc $12 ; increment row counter | inc $12 ; increment row counter | ||
| − | + | ||
lda #HEIGHT ; are we done yet? | lda #HEIGHT ; are we done yet? | ||
cmp $12 | cmp $12 | ||
Revision as of 12:51, 8 January 2020
This is a collection of simple examples of 6502 code which will run in the emulator.
Contents
Fill the Bitmapped Display
lda #$00 ; set pointer at $10 to $0200
sta $10
lda #$02
sta $11
ldx #$06 ; max value for $11
ldy #$00 ; index
loop: sta ($10),y ; store colour
iny ; increment index
bne loop ; branch until overflow
inc $11 ; increment hi byte of pointer
lda $11 ; load page number as colour
cpx $11 ; compare with max value
bne loop ; continue if not done
rts ; return
Place a Message on the Character Display
define SCREEN $f000
ldy #$00
char: lda text,y
beq done
sta SCREEN,y
iny
bne char
con e: brk
text:
dcb "6","5","0","2",32,"w","a","s",32,"h","e","r","e",".",00
Type on the Screen
; let the user type on the first page of character screen
; has blinking cursor!
; backspace works (non-destructive), arrows/ENTER don't
next: ldx #$00
idle: inx
cpx #$10
bne check
lda $f000,y
eor #$80
sta $f000,y
check: lda $ff
beq idle
ldx #$00
stx $ff
cmp #$08 ; bs
bne print
lda $f000,y
and #$7f
sta $f000,y
dey
jmp next
print: sta $f000,y
iny
jmp next
Place a Graphic on the Screen
define WIDTH 4 ; width of graphic define HEIGHT 4 ; height of graphic lda #$25 ; create a pointer at $10 sta $10 ; which points to where lda #$02 ; the graphic should be drawn sta $11 lda #$00 ; number of rows we've drawn sta $12 ; is stored in $12 ldx #$00 ; index for data ldy #$00 ; index for screen column draw: lda data,x sta ($10),y inx iny cpy #WIDTH bne draw inc $12 ; increment row counter lda #HEIGHT ; are we done yet? cmp $12 beq done ; ...exit if we are lda $10 ; load pointer clc adc #$20 ; add 32 to drop one row sta $10 lda $11 ; carry to high byte if needed adc #$00 sta $11 ldy #$00 beq draw done: brk ; stop when finished data: dcb 00,03,03,00 dcb 07,00,00,07 dcb 07,00,00,07 dcb 00,03,03,00
