Subject: Re: [stella] PAL VSYNC timings?? From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx> Date: Mon, 18 Nov 2002 14:18:00 +0100 |
Hello Dennis, >> I'm using VSYNC to check the console switches. I just couldn't resist using the 228 machine cycles in VSYNC for this. I'm also doing WSYNCs to give the 3 scan lines needed for VSYNC. I was mostly doing this because I thought that's what Eckhard meant by "uninterrupted lines". << What I meant with uninterrupted was: have the VCS do nothing but generating the sync signal by turning off the processor with WSYNCs. I was thinking of a sequence like: lda #$02 ldx #$00 sta VBLANK sta WSYNC sta VSYNC sta WSYNC sta WSYNC sta WSYNC stx VSYNC My old TV has a VHOLD knob. When I had set it a little off-tune, all PAL games and most NTSC games would play fine on the TV. Some NTSC games would roll the screen though. The only thing that all those games had in common was that they were doing something during the three lines of VSYNC. Most of them were setting the VBLANK period timer there. I don't know what exactly causes the screen rolling. It might be the accesses to the timer, accesses to the RIOT in general, or just having the VCS do anything at all. But on RGVC there were always people complaining about some of the problematical games, like Desert Falcon, rolling on their NTSC TVs, although they were 100% sure that the game was NTSC too. When I had figured out that the problem was my TV, I was able to tune the VHOLD in such a way that it would work with all games (except for Artillery Duel NTSC, which is just doing a too high frequency). Therefore I'm sure that the problem is not affecting too many TVs out there, since most of them don't have a VHOLD knob anymore. But unless you really really have to use the cycles during the VSYNC for something I'd still advice to leave the VCS alone during that time, just to be safe. >> The last I saw of this topic, Chris Wilkson was going to run some tests. Does anyone have these results? I can't find them in the archives. << Unfortunately the Atari related projects that Chris plans to do and the ones that his time allows him to actually finish aren't matching very well. And there's no-one who regrets that more than Chris himself, I'm sure. ;-) Ciao, Eckhard Stolberg ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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