Max possible graphics resolution 160 * 240 (?)

[tokra]

I've always been interested in maxing out the VIC-20 graphic powers. For years I thought 160 * 192 would be the max possible resolution.

Then I saw some of the VIC-20 demos that use the RAM in $0000-$03ff and that got me thinking. 128 x 256 is possible with putting the video-ram at $0200 or $0000 and the char-ram at $1000-$3fff - of couse BASIC is no longer an option when messing with the lower 1K. 184 x 176 is also a nice resolution possible that way.

However I always wondered if it was possible to max out all the 5K the VIC-chip can use from $0000-$03ff and $1000-$3fff (sadly the 3K block from $0400-$0fff can't be seen by the VIC even if expansion memory is present)

Anyway, I came up with a working example of a 160 * 240 resolution. This is done by using a standard 160 * 192 video and then switching the video and char ram from $1000 to $0000 at the right raster line, providing an extra 160*48 graphic and switching back once through with the extra video.

I realize this mode is probably not good for anything else than showing pictures. Calculating a pixel position is tough, since the memory layout is pretty weird.

Source code for activating the mode below. A (poor) example that fills the screen with random noise (= the recent raster line) attached as well. Load ,8,1 - start with SYS 8192 - oh yes, this is for PAL-VIC only. Actually I only tested it in VICE and would love feedback if it works on a REAL VIC.

http://www.tokra.de/vic/rasterhires.prg
http://www.tokra.de/vic/rasterhires.asm

http://www.tokra.de/vic/hiresdemo.prg

The code below was done with the VIC 20 Prog Gen. Does anyone know how to do a sta $00ec,x without having it translating to a zeropage sta $ec,x ? Any other comments/improvments on the code are welcome, I'm just starting to re-learn 6502 assembler.

Code: Select all

; Raster-Split-Hires - True 160 * 240 pixels
; only for PAL-VIC 20
; Video-Ram Top: 4096-4351 = 240 double height chars
; Char-Ram  Top: 4352-8191 = 3840 Byte = 30720 pixels(standard 160*192 res)
; Char-Ram Bottom1: 0-239 = 240 Byte = 1920 pixels
; Video-Ram Bottom: 240-299 = 60 double height chars
; Char-Ram Bottom2: 304-1023 = 720 Byte = 5760 pixels
*=$2000
	sei		; Set Interrupt Flag
	ldy	#$10
	ldx	#$00
	txa
clear1
	sta	$1000,x
	inx
	bne	clear1
	inc	clear1+2
	dey
	bne	clear1
	lda	#$10
	sta	clear1+2
	ldy	#$04
	lda	#$00
clear2
	sta	$0300,x
	sta	$9700,x
	inx
	bne	clear2
	dec	clear2+2
	dec	clear2+5
	dey
	bne	clear2
	lda	#$03
	sta	clear2+2
	lda	#$97
	sta	clear2+5
charmap1
	ldx	#$10
loop1	txa
	sta	$0ff0,x
	inx
	bne	loop1
charmap2	txa
	sta	$f0,x
	inx
	cpx	#$0f
	bne	charmap2
	ldx	#$13
loop2	txa
	byte	$9d ; sta $00ec,x (since x = $13 from $00ff)
	byte	$ec
	byte	$00
	inx
	cpx	#$40
	bne	loop2
show
	lda	#$0e
	sta	$9000
	lda	#$19
	sta	$9001
	lda	#$1f
	sta	$9003
	ldx	#$14
	stx	$9002
loop	ldy	#$cc
	sty	$9005
	ldy	#$88
	lda	#$79
raster	cmp	$9004
	bne	raster
	sty	$9005
	lda	#$91
raster2	cmp	$9004
	bne	raster2
	beq	loop

[Mike]

If you can live with a tile-based graphic display, something like 208x256 is possible, as shown in Kananga's vim VIC GUI (which was inspired by Hyper-Graphics in a 64'er special issue, FYI). Of course, not every pixel can be freely set, so this isn't a bitmap.

For a bitmapped display, however weird the address function, your idea of 160x240 seems to be the highest resolution one can get from a unmodded VIC. However ...

I realize this mode is probably not good for anything else than showing pictures.

... this pretty much sums it up, methinks.

You include the vector table at $0300 ff., especially the NMI vector at ($0318), so pressing the RESTORE key crashes the VIC. And you can neither do anything anymore with BASIC or KERNAL, as all system data is overwritten.

I've always been interested in maxing out the VIC-20 graphic powers.

It's not only a matter of putting a maximum number of pixels on-screen. Providing a dynamic display, and interoperability to BASIC, and KERNAL are also important.

Actually I only tested it in VICE and would love feedback if it works on a REAL VIC.

While I, ATM, cannot test on a real VIC-20 either, the lastest version 2.2 of VICE is pretty accurate in that regard.

[Kananga]

What is the maximum resolution that is usable on a real NTSC-Vic-20?
In Vice it is possible to set something like 24x30 characters (i.e. 192x240), but is it visible on NTSC TVs/Monitors?

[Mike]

Carlsson has posted some images of a 22, and 24 column screen of an NTSC VIC here:

http://www.sleepingelephant.com/ipw-web ... 61&start=9

Looks like 24 columns are already at the limit, and maybe 2 extra lines at top & bottom, i.e. 27 lines.