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 [ 2 posts ] 
 Interested in TTL CPU's and Designing Motherboards 
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Joined: Fri Mar 20, 2020 1:47 pm
Posts: 1
Hey folks. I'm currently teaching myself 6502 Assembly. I'm going about it in a somewhat unorthodox manner. I'm manually disassembling an old C64 game and seeing if I can reconstruct working source code. It's only an 8k cartridge game, but it's probably going to take months of effort on my part. I want to study the code, learn from it, and refactor it if I can. I'll likely publish the source when I'm done. Source code archaeology seems to be respected in the community and I haven't read of too many rights holders getting bent out of shape about it.

Farther down the road, I want to build my own TTL CPU. I want to keep the design as dead-simple as practical and experiment. It will definitely take a few queues from the 6502 though. I've also thought about building a razor-thin VM that is effectively cross-platform ASM. I have no idea who would care about such a project. The closest thing to it in real life is probably Forth, but I don't think that quite captures it. I'm still thinking about it.

I've also been inspired to see projects like the A500++. This very cool project makes me think I could (eventually) produce an open source C64 motherboard replacement and just distribute the CAD files. People could just order it printed on demand from places like PCBWay. At that point, it becomes sort of like a jigsaw puzzle with a soldering iron for nerds.

I have no idea where to start for any of that. I can barely use a soldering iron myself and I have no background in electronics. I'm just that crazy guy who *likes* assembly and wants to know *exactly* what the box is doing. None of this "I can only write code if I import 10 frameworks first" business.

Fri Mar 20, 2020 2:13 pm

Joined: Wed Jan 09, 2013 6:54 pm
Posts: 1666
Welcome! Reading code seems like a good way to learn. Disassembling and reverse engineering really tight code might be making more of a challenge, but if it's what keeps you interested then keep doing it!

The 6502 forum is of course a good place to reach lots of 6502 people - this forum here is a kind of sister forum, for all the same kinds of endeavours but with other processors - including designing new ones. So a lot of people here are also found over there.

A simple CPU is certainly a good place to start: so many projects get underwater quickly because they are too ambitious. Plenty of time later to make a less simple CPU, and then you won't be making the beginner mistakes at the same time. My favourite reference here is Thomson's Rule for First-Time Telescope Makers: "It is faster to make a four-inch mirror then a six-inch mirror than to make a six-inch mirror."

The Gigatron is a good example of a super-simple CPU which runs a more convenient VM. And in fact I think there might be as many as three VMs for it now - three flavours of accessible programming.

The thing to do, I think, is to take something which interests you enough to keep your attention, then read about that, build a simple project of an existing design, tweak it, then start to cook up your own simple project.

Fri Mar 20, 2020 8:19 pm
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