keyman64/reverse.asm at master · hbekel/keyman64 · GitHub

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/* -*- mode: kasm -*- */

/* Simple Test program for reverse keyboard scan
 * Port B is used for output and Port A for input
 * This tests wether the 7422106 is truly bidirectional
 * Exits after keypress on success, else hangs forever
*/

.pc = $c000

.var porta = $dc00
.var portb = $dc01

.var ddra = $dc02
.var ddrb = $dc03

main: {
        sei

        jsr setup

        lda #$00
        sta portb

!wait:  lda porta
        cmp #$ff
        beq !wait-

!wait:  lda porta
        cmp #$ff
        bne !wait-

        jsr reset
        cli
        rts
}

setup: {
        lda #$00 sta ddra
        lda #$ff sta ddrb
        rts
}

reset: {
        lda #$ff sta ddra
        lda #$00 sta ddrb
        rts
}