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29 lines
541 B
ArmAsm
29 lines
541 B
ArmAsm
;
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; Ullrich von Bassewitz, 07.08.1998
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;
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; unsigned char revers (unsigned char onoff);
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;
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.include "atari.inc"
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.export _revers
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.export _revflag
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_revers:
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ldx #$00 ; Assume revers off
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tay ; Test onoff
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beq L1 ; Jump if off
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ldx #$80 ; Load on value
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L1: ldy #$00 ; Assume old value is zero
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lda _revflag ; Load old value
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stx _revflag ; Set new value
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beq L2 ; Jump if old value zero
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iny ; Make old value = 1
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L2: ldx #$00 ; Load high byte of result
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tya ; Load low byte, set CC
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rts
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.bss
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_revflag:
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.res 1
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