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RE: [N8VEM-S100:353] S-100 Video board with 6845

Thanks for feedback Roger.  I agree I think this Video board is something we really have to solve to get a decent DOS baseline for future S-100 Boards (80386 etc…)  I want to try and do all further development in DOS with these  systems.   I also feel somehow it has to be 6845 (exact) hardware compatible. I just cannot find a dual ported RAM circuit to get started that does not have PAL’s (as the Lomas and CompuPro boards had) . One possibility would be to use  a later CGA “all in one” board on a chip IC. These would probably be surface mount, but there are outfits that will solder them in for you for a fee $ each.  

 Anything you come up with will be great




From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of norwe...@aol.com
Sent: Sunday, July 17, 2011 12:48 PM
To: n8vem...@googlegroups.com
Subject: Re: [N8VEM-S100:353] S-100 Vido board with 6845


Hi John,

Interesting!  The 800 lb. gorilla in the room that everybody *tries* to ignore seems to be S100 video (80x24 or 25, that is).

Perhaps there is another option besides the 6845?  Intel came out with a similar controller about the same time as Motorola introduced the 6845 - the i8275.  It has similar capabilities, I think.  There was a fellow (in Illinois, I believe) who sold a S-100 card, based on the i8275, back in the mid-80's.  The big(?) selling point was that it produced VGA video (at a time when the whole microcumputer world was moving toward IBM and MS-Doze).  I think I have one here somewhere, and maybe even a schematic and documentation?  Might take me a while to find it, however (*grin*).  I have NO idea about the availability of the i8275 anymore.  It was a 40-pin DIP.

As far as the 6845 goes, the only video circuit I ever saw was one published in "Byte", in the Ciarcia column?  Am I dreaming this?  Anybody else confirm?  Considering the source, it was most certainly NOT S-100.  *shrug*  Oh, and maybe there was another that came out in the "CRT Controller Handbook"?  Again, probably NOT S-100.   I'll have to look.

Love to hear peoples' thoughts about S-100 video.