Gigatron Hackers

Walter, I'm very sorry to hear the news. Even though I've never met Marcel, we had online chats and swapped "war stories" about our early days. I was somewhat aware of his situation, but this still comes as a shock. My deepest condolences to his family and friends. The Gigatron was the ins...

One thing that may be a factor here is the contact resistance. I had a lot of issues with my project due to the large current draw and the contact resistance of the barrel connector. The Gigatron has a much lower current consumption, but there are three contact points between the PSU and keyboard (m...

I guess it depends what you're to achieve. If the blinkenlights are enough then a simple increment ALU should give you plenty of patterns. Something that simple wouldn't be able to support the video generation though.

I always liked the idea of putting the ALU in the ROM and worked on some designs way back in the 80's. I'm bringing one to life after being inspired by the Gigatron. ROMs were pretty small back then, so I had to get creative since a single function to handle two 8-bit values takes up 64k bytes. You ...

It looks like the frequency response diagram is correct given the Gigatron component values. I think it's just the text that's swapped over. It should probably read "f_H (700Hz) > f_L (160Hz)"

I've been working on the audio amp/filters on my own project and investigating if the R2R DAC could be rolled in to the low pass filter as the input resistor. It seems to work and this is also the approach taken by the Gigatron. On closer inspection though I'm not sure the filter values look correct...

There's quite a few 6502 (and variants) soft cores available for FPGA. The cycle accurate version on Open Cores quotes 10MHz on a Spartan 3E, which is pretty obsolete at this point. You can probably get to 20MHz with the current Spartan 6 or 7.

The fundamental issue here is the additional state. You only want two states: "Pixel 1" (state A) or "Pixel 2" (state B), but there is also a third state: "Update Pixels" (state C). You can try and adjust the timing and hide state C in the A->B or B->A state transition....