RE: Joust CPU problem

Cool effect!

        I have to agree with the 161 theory. It just blindly counts up
through ram and spits the data out. The counters have certain lines which
also trigger vsync, hsync and blanking as well.

Mike

-----Original Message-----
From: David Shoemaker [mailto:davids@oz.net]
Sent: Monday, October 15, 2001 12:45 PM
To: rasterlist@synthcom.com
Subject: Re: RASTER: Joust CPU problem

I have seen this kind of problem on other boards and it usually comes down
to a 74ls161 that is not counting all the way before reset or has a stuck
line. Basically your vertical refresh clock. I am guessing (no schems
handy) that the cpu starts to read out video memory to screen and 1/2
through the refresh it looses the most significant bit and starts again from
address 0.

David
----- Original Message -----
From: "Kurt Mahan" <kmahan@xmission.com>
To: <rasterlist@synthcom.com>
Sent: Monday, October 15, 2001 8:30 AM
Subject: Re: RASTER: Joust CPU problem

> Is this a screen that is supposed to have upper islands?
>
> My guess (just a guess) would be that your vid ram address decode
> (chip selects) are hosed. I'd probe around there with a scope and
> see if you see multiple chip selects happening at once..
>
> Kurt
>
> >
> > My joust is now doing this http://www.basementarcade.com/doubejoust.JPG
> > The bottom half of the screen is repeated on the top!! The test screen
> > passes all the rom, cmos and only gives a error on one screen prior to
> > the color bar test that states something like "vertical bar error" or
> > something like that. Any ideas as I have exhausted all the William's
> > tech pages I could hunt down.
> >
> > -=Mark=-
> --------------------------------------------------------------------------
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Received on Mon Oct 15 10:30:33 2001