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cc65/libsrc/atmos/revers.s
cuz 9f547a5a4d Add basic support for ORIC Atmos
git-svn-id: svn://svn.cc65.org/cc65/trunk@2046 b7a2c559-68d2-44c3-8de9-860c34a00d81
2003-04-13 22:12:09 +00:00

38 lines
747 B
ArmAsm

;
; 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