Add revers.s

2021-03-01 22:45:05 +01:00 · 2021-03-01 22:45:05 +01:00 · abef6566e7
parent 8ec6d28f92
commit abef6566e7
1 changed files with 37 additions and 0 deletions
--- a/libsrc/telestrat/revers.s
+++ b/libsrc/telestrat/revers.s
@ -0,0 +1,37 @@
+;
+; 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
+
+