From: Charlie Carothers [mailto:csqu...@tx.rr.com]
Sent: Saturday, June 14, 2014 12:46 PM
To: Andrew Lynch
Subject: VGA chipset on S-100 bus
Hi Andrew,
I know it has been a long while - I'm *really* behind reading the classic computer emails - but I noticed just yesterday that on 8/8/13 you said:
3. S-100 TestIO V2 - An experimental S-100 to ISA bridge. The purpose
of this board is to diagnose why the VGA chipset works on the ISA bus but
not on the S-100 bus. May evolve into a general purpose bridge board
sometime in the future but is just for internal build and test at the
moment.
I was just wondering which VGA chipset you were using, and whether you got it working?
Quite a few years ago we worked through the connection of a Chips and Technology 65545 video controller to an 80386EX at work. It was not a lot of fun! Our first interface was to 320x240 quarter VGA color and mono displays. Later, we also supported a full 640x480 color display. If you've ever used an ATM with the "Tidel" logo you've seen the result (except for the very early ones which used a plasma display). Our EE (Jim) said he was told that interfacing the 65545 to the memory and address bus of the 386 was impossible, but we did it anyway. He did use a CPLD to help with some of the interface. The only thing that never quite worked correctly was reading the video RAM from the 386. I did a little diagnostic that read it and wrote it back to the same locations. When we ran that, a nice colored checkerboard would slowly turn to mush. Fortunately that was not a system requirement, so it did not really matter. Jim and I talked about it some, and he always thought he
could fix it with some CPLD changes but there was never any time available to do that since it was not critical.
We were very small fish in C&T's water, so they were not a lot of help, like zero. I remember the final connection that made it work was a pin that had to be grounded which was only explained in the data sheet for a predecessor chip!
I have no idea if you're still working on this, or if you're still having any problems with it. If you are, and there is anything I could help you with I'd be happy to try. I no longer have an operational board and display from that project, but I do have the schematics and the software source code we used. I might have a copy of the CPLD code, but I'm not sure about that.
csqu...@tx.rr.com
--
Later,
Charlie C.
@CSquared70
In God We Trust!!! (and He is in control!)