It's a neat hack. I'm almost tempted to try out this mod in dead bug style, without any PCB. The pin layout between the 2 chips match well for this. Or you can have 10 or so made for ~5 dollars excl. shipping at JLCPCB. For a smaller board, you can win some space by overlapping the "socket" with one of the IC's. As the socket can be made out of 2 rows of headers. It will still have a volume conflict with the
prototype SPI expander. [
Edit: Perhaps make it a wider board that extends above the video resistors?] I would also rotate U2 by 180 degrees so it faces left like all other ICs.
The bit assignment needs some extra thought. Low resolution is like this:
Code: Select all
bit 76543210
VH------ sync
--BBGGRR big pixel
[Indeed: the Gigatron has the RGB order reversed compared to common conventions. It was way too late to change it once we noticed this, with kits already out there...]
High resolution could be like this:
Code: Select all
bit 76543210
VH------ sync
--b-g-r- left pixel
---b-g-r right pixel
But then with 'r' being #aa0055, 'g' #55aa00 and 'b' #0055aa (web notation).
The idea of interleaving the pixels is two-fold:
- Color components from low resolution images map to related hues when displayed in high resolution
- In software it's easier to shift-left by 1 bit than to shift-left by 3 bits
I expect the colors will come out in this order, from low to high:
- palette-8c.png (350 Bytes) Viewed 8701 times
I did left/right pixel in big-endian bit order, but it can just as easy be reversed. I see no strong compelling reason for either order yet.
- modded.gif (53.25 KiB) Viewed 8710 times
Or directly wired, perhaps like this. It's a lot of wires for a small space...
- deadbug.png (105.61 KiB) Viewed 8710 times