6502 Keycheck

; Labels

PRA  =  $dc00            ; CIA#1 (Port Register A)
PRB  =  $dc01            ; CIA#1 (Port Register B)

; main loop to detect keypresses

keycheck
        lda #$7f        ; test $DC00 bit row 7 ($7F)
        sta PRA
        lda PRB

        cmp #$fe        ; key '1' pressed?
        beq playtune1   ; then play tune 1 routine

        cmp #$f7        ; key '2' pressed?
        beq playtune2   ; then play tune 2 routine

                        ; now swap to different row!
        lda #$fd        ; test $DC00 bit row 1 ($fd)
        sta PRA
        lda PRB

        cmp #$fe        ; key '3' pressed?
        beq playtune3   ; then play tune 3 routine

        jmp keycheck

;routines to play each tune after keypress detection

playtune1
        lda #$00        ; set tune 1
        jsr music+$00   ; reinitialise player
        jmp keycheck    ; back to keycheck loop

playtune2
        lda #$01        ; set tune 2
        jsr music+$00   ; reinitialise player
        jmp keycheck    ; back to keycheck loop

playtune3
        lda #$02        ; set tune 3
        jsr music+$00   ; reinitialise player
        jmp keycheck    ; back to keycheck loop