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48 lines
1.9 KiB
ArmAsm
48 lines
1.9 KiB
ArmAsm
;
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; unsigned char kbhit (void);
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;
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; The method to detect a pressed key is based on the documentation in
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; "Section 3 Programmed Key Functions" in "The Challenger Character Graphics
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; Reference Manual"
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; We only want to return true for characters that can be returned by cgetc(),
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; but not for keys like <Shift> or <Ctrl>. Therefore a special handling is
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; needed for the first row. This is implemented by a bit mask that is stored
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; in tmp1 and that is set to zero after the first round.
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;
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.export _kbhit
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.include "osic1p.inc"
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.include "extzp.inc"
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.include "zeropage.inc"
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_kbhit:
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lda #%11011111 ; Mask for only checking the column for the
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sta tmp1 ; ESC key in the first keyboard row.
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lda #%11111110 ; Mask for 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 tmp1 ; Mask out uninteresting keys (only relevant in
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; first row)
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cmp #$FF ; No keys pressed?
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bne keypressed
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lda #$00 ; For remaining rows no keys masked
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sta tmp1
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txa ; Restore A
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sec ; Want to shift in ones
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rol a ; Rotate row select to next bit position
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cmp #$FF ; Done?
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bne scan ; If not, continue
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lda #$00 ; Return false
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tax ; High byte of return is also zero
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sta CHARBUF ; No character in buffer
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rts
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keypressed:
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jsr INPUTC ; Get input character in A
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sta CHARBUF ; Save in buffer
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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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