cc65/libsrc/creativision/clrscr.s

;*
;* clrscr
;*
;* NB: All screen functions assume Graphics Mode 1 in a default configuration.
;* Therefore, this is hard coded to use $1000-$12FF as screen VRAM.

        .export         _clrscr
        .include        "creativision.inc"

_clrscr:

        sei             ; Disable interrupts. Default INT handler reads VDP_STATUS
                        ; and would lose any setup done here.

        lda     #$00    ; VRAM offset low
        sta     VDP_CONTROL_W

        lda     #$50    ; VRAM offset high ($10 OR $40)
        sta     VDP_CONTROL_W

        lda     #$40    ; Space char from ROM setup

        ldx     #0
        ldy     #3

L1:     sta     VDP_DATA_W
        inx
        bne     L1
        dey
        bne     L1

        cli             ; Let interrupts go again

        lda     #0
        sta     CURSOR_X
        sta     CURSOR_Y
        sta     SCREEN_PTR
        lda     #$10
        sta     SCREEN_PTR+1

        rts
Initial Creativision Import 2013-12-05 11:40:44 +00:00			`;*`
			`;* clrscr`
			`;*`
			`;* NB: All screen functions assume Graphics Mode 1 in a default configuration.`
			`;* Therefore, this is hard coded to use $1000-$12FF as screen VRAM.`

Cleanups for Creativision. 2017-02-01 18:46:04 +00:00			`.export _clrscr`
			`.include "creativision.inc"`

Initial Creativision Import 2013-12-05 11:40:44 +00:00			`_clrscr:`

Cleanups for Creativision. 2017-02-01 18:46:04 +00:00			`sei ; Disable interrupts. Default INT handler reads VDP_STATUS`
			`; and would lose any setup done here.`

			`lda #$00 ; VRAM offset low`
			`sta VDP_CONTROL_W`

			`lda #$50 ; VRAM offset high ($10 OR $40)`
			`sta VDP_CONTROL_W`

Creativison changes. This change includes some cleanups, removal of mainargs.s (game console programs never have arguments), and a workaround for a problem I'm seeing. The problem is that sometimes (in fact, more often than not) the clrscr() call in testcode/lib/joy-test.c writes some garbage chars on the screen (most often a "P"). Could be my hardware (I haven't seen it on MAME), but to me the root cause is still unknown. 2017-03-17 20:42:51 +00:00			`lda #$40 ; Space char from ROM setup`
Cleanups for Creativision. 2017-02-01 18:46:04 +00:00
			`ldx #0`
			`ldy #3`

			`L1: sta VDP_DATA_W`
			`inx`
			`bne L1`
			`dey`
			`bne L1`

			`cli ; Let interrupts go again`

			`lda #0`
			`sta CURSOR_X`
			`sta CURSOR_Y`
Creativison changes. This change includes some cleanups, removal of mainargs.s (game console programs never have arguments), and a workaround for a problem I'm seeing. The problem is that sometimes (in fact, more often than not) the clrscr() call in testcode/lib/joy-test.c writes some garbage chars on the screen (most often a "P"). Could be my hardware (I haven't seen it on MAME), but to me the root cause is still unknown. 2017-03-17 20:42:51 +00:00			`sta SCREEN_PTR`
Cleanups for Creativision. 2017-02-01 18:46:04 +00:00			`lda #$10`
Creativison changes. This change includes some cleanups, removal of mainargs.s (game console programs never have arguments), and a workaround for a problem I'm seeing. The problem is that sometimes (in fact, more often than not) the clrscr() call in testcode/lib/joy-test.c writes some garbage chars on the screen (most often a "P"). Could be my hardware (I haven't seen it on MAME), but to me the root cause is still unknown. 2017-03-17 20:42:51 +00:00			`sta SCREEN_PTR+1`
Cleanups for Creativision. 2017-02-01 18:46:04 +00:00
			`rts`