[Coco] Disto SC add-ons
gene.heskett at verizon.net
Fri Jan 2 20:19:09 EST 2009
On Friday 02 January 2009, Roger Taylor wrote:
>At 12:35 AM 1/2/2009, you wrote:
>>Try this link Roger:
>>The article is called "Increasing Character Display".
>I suppose the article came before Tony actually built the SC version
>of that project. I'm not sure the board is worth messing with right
>now considering I still don't know what header pins the video signals
>are on and exactly what type of monitor (obtainable today) would work
>with it. It does sound ideal for giving 80 columns on a CoCo 1/2
>from OS-9, or giving dual 80-column displays on a CoCo 3.
I don't happen to have a set of specs on that particular crt controller Roger,
but I would suspect a simple doubling of the dot clock crystal would make it
compatible with vga, which needs a minimum h rate of 31.5Khz. That would
make it a 29 Mhz crystal I believe. That might however, need a 2x faster
character data rom too. My WP-RS was running on the usual 14.x Mhz crystal,
but with reworked blanking and sync times so it ran at about 18Khz h rate,
and 70 Hz v rate. A Maggy 12" PC Monitor 80 was happy as a clam running at
that speed for over a decade once the h oscillator coil slug was backed out
for the higher sweep rate. That all served to make the display much bigger
and more easily read, which was the main idea.
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