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29 lines
1003 B
ArmAsm
29 lines
1003 B
ArmAsm
;
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; unsigned char kbhit (void);
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;
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.export _kbhit
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.include "osic1p.inc"
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_kbhit:
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lda #%11111110 ; Select first keyboard row
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scan:
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sta KBD ; Select keyboard row
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tax ; Save A
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lda KBD ; Read keyboard columns
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ora #$01 ; Mask out lsb (Shift Lock), since we ignore it
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cmp #$FF ; No keys pressed?
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bne keypressed
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txa ; Restore A
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sec ; Want to shift in ones
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rol a ; Rotate row select to next bit position
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cmp #$FF ; Done?
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bne scan ; If not, continue
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ldx #$00 ; High byte of return is always zero
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lda #$00 ; Return false
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rts
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keypressed:
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ldx #$00 ; High byte of return is always zero
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lda #$01 ; Return true
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rts
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