Gigatron Hackers

I did a quick scan of The V5a ROM to see what Instructions were used That's really helpful. I also noticed 6 instances of "bra [Imm]". Those I could handle, but not the "jmp [Imm]". I agree with @at67 though. Breaking compatibility is a rabbit hole I don't want to go down. I jus...

Another week of humiliation :lol: One apparent optimization of the Gigatron design is replacing U32 and U33 (zero page multiplexer) with a pull-down resistor. The Y register is changed to a tristate latch and the EH signal is inverted and used as the ~OE. The pull-down will select the zero page with...

Do you have an unused input pin on the same GAL to replicate the same mechanism? That's basically what I have now, but any path through the GAL is more than just a single gate. It does look like I've solved that issue though. I'm dividing down a 25.175 MHz to 6.25ish using a two-stage ring counter ...

take 2 Gigatrons, use a 2-phase clock, and connect them at the memory. The memory would then become a bottleneck. One Gigatron would have to halt while the other execute, slowing each to half the speed. You would be duplicating the registers and ALU with no real benefit here. There would also be sh...

Step one... enter the schematic correctly
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Behold the "Novatron"! I forgot to order the ZIF socket of course... so I'll have to stop here until after the weekend. Clock is running and the program counter is counting.
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I've only used GALs (which are reprogrammable) before, but I thought that PALs were OTP? I usually use GALs, specifically the ATF16V8B for development. I try and stick within the original PAL specs so you could build it with the vintage parts. I do have some NOS PALs for another project, but I stil...

Mostly routed. I was going to test the new design on a breadboard, but the only real change are the PALs. These can be reprogrammed so most of the debugging will be in firmware... assuming I didn't screw up the schematic. The ATtiny85 is on the board for the basic Pluggy, so it can be built to match...

Initial chip placement. The connectors and associated components haven't been added yet; they would go along the bottom edge. The gap is for the Pluggy Reloaded components. I left the option to use the existing Pierce Oscillator/6.25MHz crystal or you can use the can oscillator and divider (bottom l...

Video Repeater : https://forum.gigatron.io/viewtopic.php?t=303 I think I'm going to go with the video repeater, at least layout the components on the board as an option. The FIFOs are kind of pricey but not crazy and they are still in production. The ALU won't fit in a pair of 16L8 PALs. It probabl...