cc65/libsrc/pet/clrscr.s

;
; Ullrich von Bassewitz, 26.11.1998
;
; void clrscr (void);
;

        .export         _clrscr
        .import         plot
        .importzp       ptr1

        .include        "pet.inc"

_clrscr:

; Set the screen base address

        lda     #$00
        sta     ptr1
        lda     #$80
        sta     ptr1+1

; Determine, how many pages to fill

        ldx     #4
        lda     SCR_LINELEN     ; Check length of one line
        cmp     #40+1
        bcc     L1
        ldx     #8

; Clear the screen

L1:     lda     #$20            ; Screen code for blank
        ldy     #$00
L2:     sta     (ptr1),y
        iny
        bne     L2
        inc     ptr1+1
        dex
        bne     L2

; Set the cursor to 0/0

        lda     #0
        sta     CURS_X
        sta     CURS_Y
        jmp     plot

        rts