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Add revers.s

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jede 2021-03-01 22:45:05 +01:00
parent 8ec6d28f92
commit abef6566e7
1 changed files with 37 additions and 0 deletions
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libsrc/telestrat/revers.s Normal file
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;
; Ullrich von Bassewitz, 07.08.1998
;
; unsigned char revers (unsigned char onoff);
;
.export _revers
.export rvs
; ------------------------------------------------------------------------
;
.code
.proc _revers
ldx #$00 ; Assume revers off
tay ; Test onoff
beq L1 ; Jump if off
ldx #$80 ; Load on value
ldy #$00 ; Assume old value is zero
L1: lda rvs ; Load old value
stx rvs ; Set new value
beq L2 ; Jump if old value zero
iny ; Make old value = 1
L2: ldx #$00 ; Load high byte of result
tya ; Load low byte, set CC
rts
.endproc
; ------------------------------------------------------------------------
;
.bss
rvs: .res 1