Modified Gigatron Design Ideas

Using, learning, programming and modding the Gigatron and anything related.
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marcelk
Posts: 431
Joined: 13 May 2018, 08:26

Re: Modified Gigatron Design Ideas

Post by marcelk » 24 Nov 2019, 04:35

The '244 is just a tri-state buffer, not a register, not even a latch. You can find a really good explanation here. This video is part of the Ben Eater youtube series that goes through all steps of building an 8-bit breadboard computer. It is a very good resource for you as well. There are 44 videos where he explains the details of every TTL chip and how it is used. Many of his part numbers, or their cousins, come back in the Gigatron in a similar role. For under $300 he also sells everything you need to build his computer yourself. It can calculate Fibonacci numbers and you can see every step.

PurpleGirl
Posts: 38
Joined: 09 Sep 2019, 08:19

Re: Modified Gigatron Design Ideas

Post by PurpleGirl » 25 Nov 2019, 06:04

So a 377 or 2 161's might be better for what I have in mind, though a tristate buffer might work if the data is streamed. So it depends on the application. But adding opcodes, I think I'd want an X-Out rather than a load.

PurpleGirl
Posts: 38
Joined: 09 Sep 2019, 08:19

Re: Modified Gigatron Design Ideas

Post by PurpleGirl » 18 Jan 2020, 18:24

I've been thinking about Ben Eater's "video card" design. I was pondering how to modify it to where the syncs could be modified by software. I think I've discovered a way to do that. Instead of using hardwired logic gates, a register and a digital comparator would be better. So the pixel counter setpoints for the porches could be placed into the registers. Then the comparators would trigger the latches to toggle the syncs for the porches based on the values in the registers. While that would ideally take a microprocessor, jumpers could work.

Now, I've been pondering on how to make a video board. I know the basics about how to do a pixel counter and do the latches and syncs. I could put RAM on the board. The pixel counter would not only control the latches but would also do the addressing of the video memory. A shift register could be used to buffer the output, thus the buffer could hold the memory. However, even then, the same problem would present itself, and that is how to get the data out of the memory.

So using 2 memory banks that flip could work, but that introduces another problem. The banks could get considerably out of sync. If you add other mods such as adding the ability to update single lines or pixels, then the entire page won't be overwritten on the memory that's being used for output. So that could cause artifacts, flicker or display corruption. So one workaround would be to write to the current output bank if/when the input address is the same as the output address. Another workaround would be to write to the current output bank during the porches.

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