[Coco] FW: CoCo2 lower graphics

Ciaran Anscomb cocomalt at 6809.org.uk
Sun Jun 19 02:33:11 EDT 2016

"Michael Pittsley" wrote:
> I was unable to send this to the group due to the attachments being too
> large.   Any additional assistance you could give would be greatful.

Hope you don't mind, I'll reply to the list, and have uploaded the
jpegs here:


> I'm not really sure how to respond to these messages on here.  I hope I have
> it right.  Anyhow.  Running screen0,1 goto 10 doesn't do much.  From the TV
> I have the CoCo connected to, it presents an orange line that runs up and
> down the screen until I press break.  Attached see the screen shots or what
> I am talking about  the lower / bottom half the graphics not working.

So to me the Frogger shot looks like a low-res mode is being presented
as hi-res.  The VDG itself doesn't do this, it's the SAM that handles
the addressing, so if possible I'd try replacing that chip (6883,
SN74LS783/5) - everything else the SAM does looks like it's working
so I'd guess at some internal fault just limited to the video address
counters or divisor selection.


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