Up, down, left and right all work as they should. Any combination of three buttons or more works as expected (opposite directions cancel each other out, up+down+left+right results in no movement). Down+left and down+right also work as expected.
Up+left, however, results in movement up, no left, and up+right results in movement up and double movement right.
Any ideas?
Code: Select all
readctrl:
lda #$01
sta $4016
lda #$00
sta $4016
; Read all 8 buttons
ldx #$08
loop:
pha
; Read next button state and mask off low 2 bits.
; Compare with $01, which will set carry flag if
; either or both bits are set.
lda $4016
and #$03
cmp #$01
; Now, rotate the carry flag into the top of A,
; land shift all the other buttons to the right
pla
ror a
dex
bne loop
tax
txa
and #$10 ; up
beq :+
lda #$ff
adc $0204
sta $0204
: txa
and #$20 ; down
beq :+
lda #$01
adc $0204
sta $0204
: txa
and #$40 ; left
beq :+
lda #$ff
adc $0207
sta $0207
: txa
and #$80 ; right
beq :+
lda #$01
adc $0207
sta $0207
lda #$02
sta $4014 ; OAM DMA from RAM page 2
