Key listener

; run every frame in interrupts IM 2
keyListener:
    call getAKey
    ld a,r
    sub 3
    ret z   ; key not pressed
    sub 4
    rra
div5:
    rrc b
    jr nc,getChar
    sub 3
    jr div5
getChar:
    add a,low rows
    ld l,a
    adc a,high rows
    sub l
    ld h,a
;   ld l,a
;   ld h,0
;   ld bc,rows
;   add hl,bc
    ld a,(hl)   ; received char (key)
    // .....
    ret
getAKey:
    ld   bc,#FEFE
    xor a
    ld r,a
nextRow
    in   a,(c)
    cpl
    rrca
    ret c
    rrca
    ret c
    rrca
    ret c
    rrca
    ret c
    rrca
    ret c
    rlc  b
    jr c,nextRow
    ret
rows:
    db "}ZXCV"
    db "ASDFG"
    db "QWERT"
    db "12345"
    db "09876"
    db "POIUY"
    db "{LKJH"
    db "^`MNB"