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50 lines
1.2 KiB
Plaintext
50 lines
1.2 KiB
Plaintext
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processor 6502
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org $7ffe
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word $8000 ; load address
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; cartridge header (http://swut.net/c64cart-howto.html)
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.byte $09, $80, $25, $80
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.byte $c3, $c2, $cd, $38, $30
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.byte $8e, $16, $d0, $20, $a3, $fd, $20
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.byte $50, $fd, $20, $15, $fd, $20, $5b
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.byte $ff, $58
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.byte $ea, $ea, $ea, $ea, $ea, $ea, $ea
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.byte $ea, $ea, $ea, $ea, $ea
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; program start
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Temp equ $00
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Start
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sei ; turn off interrupts
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ldy #0
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sty $d020 ; reset border color
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Loop
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lda Message,y ; load message byte
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beq EOM ; 0 = end of string
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clc
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adc #$c0 ; + 192
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sta $400+41,y ; store to screen
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iny
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bne Loop ; next character
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EOM
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Wait1
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lda $d011
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bmi Wait1 ; wait for line < 256
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Wait2
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lda $d012 ; get current scanline
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Wait3
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cmp $d012
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beq Wait3 ; wait for scanline to change
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lsr
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lsr
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clc
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adc Temp
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sta $d020 ; set border color
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lda $d011 ; get status bits
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bpl Wait2 ; repeat until line >= 256
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sty $d020 ; reset border color
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dec Temp ; scroll colors
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jmp Wait1 ; endless loop
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Message
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; PETSCII - http://sta.c64.org/cbm64pet.html
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byte "HELLO`WORLDa"
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byte 0
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