another joystick test, bitwise, looped, with comments too (c64)

joyloop.asm

; minimal joystick test #3, 21 bytes loop version; @ = not set, A = set

        * = $1000

INIT    LDY #8          ; init loop for checking all joystick port bits
        LDA $DC00       ; load joystick port byte

LOOP    PHA             ; make a copy and put it on the stack
        AND #1          ; least significant bit set?
        STA $0400,Y     ; put either 0 or 1 (poke code) on screen
        PLA             ; get joystick byte back from stack
        LSR             ; shift right to get next bit
        DEY             ; y = y - 1
        CPY #0          ; explicit test to have a correctly set zeroflag
        BNE LOOP        ; finished inner loop?
        JMP INIT        ; all bits checked. get a fresh load.