read:	ldx #01h

loop2:  ldy #09h 
	sty 4016h
	dey
	sty 4016h

loop:   lda 4016h,x
        lsr a
        rol buttons,x
        dey
        bne loop
        lda buttons,x
        pha
        eor oldbuts,x
        and buttons,x
        sta pressed,x
        pla
        sta oldbuts,x
        dex
        bpl loop2
        rts


RAM variables:

;first byte is controller 1,  second byte is controller 2.

buttons:  .dsb 2  ;reserve 2 bytes for current state of the buttons
oldbuts:  .dsb 2  ;reserve 2 bytes for old state of the buttons
pressed:  .dsb 2  ;reserve 2 bytes for which buttons were just pressed