VGA

I've been trying to work out what the highest rez I can fit into my Jupiter Ace Clone. After a bit of messing around, I think I can use a 4k dual-ported RAM paged into a 1K window for 80x51 chars with 8x8 chars. The underlying resolution would be 640x408 but not pixel addressable. This is my first bash at a schematic. It's right at the limit of speed capabilities for 7400 logic and memory at 25.2 Mhz. So it got a type of buffer/cache that I think I remember seeing in a hardware lecture many years ago.

Any comments? See PDF of Schematic or  a Git on GitHub.

Various people have commented that I'm being a bit pessimistic with the timings and that the chances of the chips taking the maximum time outlined in their specifications. Without the chips to test and measure, there is little chance of getting optimal performance.

One thing this has made me do is to overcome my avoidance of GALs and other programmable logic. The one clear thing is that the tools available are a pain.





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