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247c29f7a5
INVFLG is changed by the Atari key git-svn-id: svn://svn.cc65.org/cc65/trunk@16 b7a2c559-68d2-44c3-8de9-860c34a00d81
29 lines
543 B
ArmAsm
29 lines
543 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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.data
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_revflag:
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.byte 0
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