asm 6502 Copy Bit x on Y

; Zero page free bytes
ZPFB    = $FB
ZPFC    = $FC



*=$0801

    BYTE    $0E, $08, $0A, $00, $9E, $20, $28,  $32, $30, $36, $34, $29, $00, $00, $00

        ; Test
        lda #%11111110          ; Value
        ldx #1                  ; Source bit 1
        ldy #0                  ; Target bit 0
        jsr CopyBitXOnY         ; Call Generic copy bit routine
        sta $0400               ; print raw result code  255
        rts

Mask
        byte %11111110          ; 0
        byte %11111101          ; 1
        byte %11111011          ; 2
        byte %11110111          ; 3
        byte %11101111          ; 4
        byte %11011111          ; 5
        byte %10111111          ; 6
        byte %01111111          ; 7

;******************************************************************************
; CopyBitXOnY
; A = Value
; X = Source bit
; Y = Target bit
; return
; A with Target bit equal to Source Bit
;******************************************************************************
CopyBitXOnY
        sta ZPFB                ; Save value
        lda Mask,y              ; load target reset Mask
        and ZPFB                ; reset target bit
        sta ZPFB                ; save Value
        lda Mask,x              ; Load source reset Mask
        eor #$ff                ; change it on source set mask
        and ZPFB                ; test source bit
        beq CB_Exit             ; if zero then exit
        lda Mask,y              ; load target reset Mask
        eor #$ff                ; change it on target set mask
        ora ZPFB                ; set target bit
        rts

CB_Exit
        lda ZPFB                ; load value
        rts