[Coco] Disto SC add-ons

[Gene Heskett]

On Friday 02 January 2009, Roger Taylor wrote:
>At 12:35 AM 1/2/2009, you wrote:
>>Try this link Roger:
>>
>><ftp://maltedmedia.com/coco/VARIOUS/TUTORIALS/HARDWARE/FULLTURN/SECTIONS/Fu
>>llTurn_P125_134.pdf>
>>
>>The article is called "Increasing Character Display".
>>
>>Darren
>
>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.

-- 
Cheers, Gene
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