File: revers.s

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;
; Ullrich von Bassewitz, 07.08.1998
;
; unsigned char revers (unsigned char onoff);
;

        .export         _revers

        .include        "pet.inc"

.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