02 - Tutorial Two.asm

; 10 SYS (2304)

*=$0801

        BYTE    $0E, $08, $0A, $00, $9E, $20, $28
        BYTE    $32, $33, $30, $34, $29, $00, $00, $00

;*******************************************************************************
;* Reverses the screen                                                         *
;*                                                                             *
;* Written By John C. Dale                                                     *
;* Tutorial #02                                                                *
;* Date : 28th Dec, 2016                                                       *
;*                                                                             *
;*******************************************************************************
;*                                                                             *
;*******************************************************************************

*=$0900
SCRN_START=$0400

defm ReverseScreenLocation
    lda /1,x
    eor #128
    sta /1,x
    endm

    ldx #0          ; Initialise Offset
LOOP
    ReverseScreenLocation SCRN_START ; Screen Bank 0
    ReverseScreenLocation SCRN_START + $0100 ; Screen Bank 1
    ReverseScreenLocation SCRN_START + $0200 ; Screen Bank 2
    ReverseScreenLocation SCRN_START + $0300 ; Screen Bank 3
    inx
    bne LOOP
    rts