sty VIA1_DDRA ; restore the state of DDRA
cli ; necessary?
- ror ; Shift sw3 into bit 7
- and #$9E ; Mask relevant bits
- eor #$9E ; Active states are inverted
+ php ; Save sw3 in carry
+ lsr ; Shift sw0,sw1,sw2,sw4 into bits 1-4
+ tax ; Save sw0,sw1,sw2
+ and #$10 ; Extract sw4 in bit 4
+ sta tmp1 ; Save sw4 in bit 4
+ txa ; Restore sw0,sw1,sw2
+ lsr ; Shift sw0,sw1,sw2 into bits 0-2
+ and #$07 ; Mask bits 0-2
+ plp ; Restore sw3 in carry
+ bcc @L0 ; Is sw3 set?
+ ora #$08 ; Yes: Add sw3 in bit 3
+@L0: ora tmp1 ; Add sw4 in bit 4
+ eor #$1F ; Active states are inverted
+ ldx #0
rts
; Read joystick 2
sta VIA1_PRB ; (output one at PB7)
lda VIA1_PRB ; via port B read/write
- and #$1f ; get bit 4-0 (PB4-PB0)
- eor #$1f
+ and #$1F ; get bit 4-0 (PB4-PB0)
+ eor #$1F
rts
; Read joystick 3
sta VIA1_PRB ; (output zero at PB7)
lda VIA1_PRB ; via port B read/write
- and #$0f ; get bit 3-0 (PB3-PB0)
+ and #$0F ; get bit 3-0 (PB3-PB0)
sta tmp1 ; joy 4 directions
lda VIA1_PRB ; via port B read/write
and #%00100000 ; get bit 5 (PB5)
lsr
ora tmp1
- eor #$1f
+ eor #$1F
ldx #0
rts
sty VIA1_DDRA ; restore the state of DDRA
cli ; necessary?
- ror ; Shift sw3 into bit 7
- and #$9E ; Mask relevant bits
- eor #$9E ; Active states are inverted
-
+ php ; Save sw3 in carry
+ lsr ; Shift sw0,sw1,sw2,sw4 into bits 1-4
+ tax ; Save sw0,sw1,sw2
+ and #$10 ; Extract sw4 in bit 4
+ sta tmp1 ; Save sw4 in bit 4
+ txa ; Restore sw0,sw1,sw2
+ lsr ; Shift sw0,sw1,sw2 into bits 0-2
+ and #$07 ; Mask bits 0-2
+ plp ; Restore sw3 in carry
+ bcc @L0 ; Is sw3 set?
+ ora #$08 ; Yes: Add sw3 in bit 3
+@L0: ora tmp1 ; Add sw4 in bit 4
+ eor #$1F ; Active states are inverted
+
+ ldx #0
rts