ACME test for Command X16

test.asm

; comppile with ACME (https://sourceforge.net/projects/acme-crossass/ ) 
; acme -f cbm -o test.prg test.asm
;
; then start in the emulator:
; x16emu -run test.prg

*=$0801

        !byte $0b,$08,$01,$00,$9e,$32,$30,$36,$31,$00,$00,$00

        sei
        lda #4
        sta $9F20
        lda #0
        sta $9F21
        sta $9F22
        lda #33
        sta $9F23
        lda #2
        sta $9F21
loop:   sta $9F23
        eor #$FF
        jmp loop