[CC] [CHIPER] Moving Pixel

; refresh screen
ld I, $FFF
ld (I), $1
; ---------------------

; set screen text color to black
ld I, $FFD
ld (I), $F
; ---------------------

.loop

; this will fix any trailing behind the pixel
ld A, $20
ld I, $FFE
ld (I), A
; ---------------------

call updatePixel	; call the update pixel function

; show the pixel
ld A, $81			; this is the pixel HEX value
ld I, $FFE
ld (I), A
; ---------------------

; refresh screen
ld I, $FFF
ld (I), $1
; ---------------------

jmp loop			; loop back

.updatePixel

ld I, $FF9			; load the current key pressed
ld A, (I)			; store it in register A
ld B, #0			; reset B to 0 (so we would not add B always)
add B, A 			; move A to B
eql A, $3			; check if its Left key
call left 			; if true call .left
eql A, $4			; check if its Right key
call right			; if true call .right
eql A, $1			; check if its Up key
call up 			; if true call .up
eql A, $2			; check if its down key
call down 			; if true call .down

ret

.left				; left movement

; load screen X pos and update it
ld I, $FFA
ld A, (I)
sub A, #1
ld (I), A
; ---------------------

call resetKey		; reset the key
ret

.right				; right movement

; load screen X pos and update it
ld I, $FFA
ld A, (I)
add A, #1
ld (I), A
; ---------------------

call resetKey		; reset the key
ret

.up					; up movement

; load screen Y pos and update it
ld I, $FFB
ld A, (I)
sub A, #1
ld (I), A
; ---------------------

call resetKey		; reset the key
ret

.down				; down movement

; load screen Y pos and update it
ld I, $FFB
ld A, (I)
add A, #1
ld (I), A
; ---------------------

call resetKey		; reset the key
ret

.resetKey

; moves B value to A
ld A, #0
add A, B
ret