;
; How to set up screen mode with BIOS?
; Featuring also VDP writing and keyboard reading.
; Note that TASM doesn't know about precedence in arithmetic.
;
; - Marq/L!T

PIXELS  .equ    0 ; Address of pixels in VRAM

.org	100h

	ld	a,3	; SCREEN 3 (64x48 gfxmode)
	ld      (0fcafh),a
	ld	ix,05fh
	ld	iy,(0fcc0h)
	call	01ch	; Inter-slot call

	ld	d,0

mainloop:
	halt		; Wait for vertical blank

	ld	a,PIXELS & 0ffh ; Set write address to VDP
	out	(099h),a
	ld	a,PIXELS >> 8
	or	040h
	out	(099h),a

	ld	bc,32*48 ; We'll write 64*48 pixels (1 byte=2 pixels)

filloop:
	ld	a,d	
	out	(98h),a	; Write fill byte to VRAM. VDP increases the address
	dec	bc	; automatically
	ld	a,b
	or	c
	jp	nz,filloop ; Over and over

	inc	d	; Increase fill byte

	in	a,(0aah) ; Check whether space is pressed
	and	0f0h
	or	8
	out	(0aah),a
	in	a,(0a9h)
	and	1
	jp	nz,mainloop ; Not pressed, keep on keeping on
	
	xor	a	; SCREEN 0 (40x24 textmode)
	ld	(0fcafh),a
	ld	ix,05fh
	ld	iy,(0fcc0h)
	call	01ch	; Inter-slot call

	ret	; Back to DOS

.end