I always applaud homebrew cpu designs but after doing so many myself I would reaaaaly advice to stay away from dip chips/breadboards/wirewraps and any attempts to put it into real physical world. Taking a build out of a logisim/verilog to real world in chips sucks away all the fun about cpu design - suddenly you have to deal with invisible issues like timing, glitchy half-dead chip, bad wire connection, etc. these are not challenges, just mundane dull work.
The only exception to „stay in the sim“ rule is if you want to make an „art statement“, i.e. like BMOW (or my relay cpu https://github.com/artemonster/relay-cpu/blob/main/images/fr... /shamelessplug)
> It’s a standalone tool that lives outside the computer. I put the EEPROM into the socket, and connect via serial to my laptop to upload the binary files.
Huh, I guess I never really thought about it, but how did they program the first CPUs? Like how did they overcome the chicken/egg situation?
To get both blinkenlights for registers and tri-state for bus driving, use two ’574 chips in parallel rather than a ’377 behind a ’245. Tie the clock and input lines together on both. Tie the output enable low on the one driving the blinkenlights. This way the chip that the rest of the CPU depends on doesn’t have the extra work of driving any load and you only have one chip’s worth of propagation delays.
Hi Will, absolutely amazing this, I love the 'money shot' up front, there are days my desk and yours could be swapped without either of us realizing right away what happened.
The Rigol deserves a blog post of its own, I've got one too and the better I get in using it the more I'm amazed at what it can do.
I've run into the same 'all you can get is SMD' which is fine for when you're finished but a lot harder while you're still figuring things out. This is where 'proper engineers' can go straight to the finish line and I always struggle.
You also develop some kind of sixth sense for when something is misbehaving. If you haven't read it yet, 'The Soul of a New Machine' might be to your liking.
Of course while you're doing the next version you should knock out a tiny tapeout version, it should easily fit in a single cell (maybe 2 if you want to push the 256 byte sram in as well)
Hello Will, interesting read, and happy to see 8-bit breadboard builds on HN. I used to follow Ben and James years ago and built a fully functional 256-byte ROM/RAM cpu that could accept instructions from Arduino as a IO input. I gave up on extending output to add a mini OLED.
Cool to see your project and can't wait for part 4.
The first image I saw gave me considerable anxiety and dread lol. I am so impressed, and have always wanted to do something like this. I took a digital logic course in university that was an absolute blast. I never wanted to stop there, but ultimately ended up doing so. However, just looking at all those wires made me feel a sense of, "Maybe I won't do this after all."
You have to be a little mad to do this but exceptionally mad to do it on at least 8 independent breadboards using no less than 4 different styles of jumper wire!
The unfortunate reality of building these home-brew CPUs is that almost all of the "medium integration" ICs are long out of production - things like the 74181 ALU slice, carry lookahead adders, 16-way register files, etc.
Makes doing things larger than 8/16 bit computers very complicated and usually very slow :(
This is very cool. And I found it timely since I also have embarked on a similar journey to build an analog computer—and gone through similar steps of breadboarding, ordering PCBs (iterating and iterating).
And no shit, Claude has helped with a lot of the EE stuff that I was only semi-knowledgeable about. I want to pursue a multiplier unit using log/anti-log circuits and an LLM suggests multiplying with PWM. For another module I complain about the cost of a 16-bit ADC and the LLM suggests a 12-bit drop-in replacement that costs half as much. I want sine and cosine and the LLM suggests using diodes/resistors to "shape" a voltage to approximate a sine curve—rattles off the resistor values needed.
I breadboard first everything the LLM suggests, dig around on the internet to see if the idea is legit/sound, and in the process have learned an enormous amount about electronics in general.
When you design the final board, consider making two boards - one for all your logic, and a separate one for all your user-facing I/O - blinkenlights, toggles, buttons, and so on, with something like a ribbon cable connection for them. Being able to separately mount your I/O from your logic board gives you more freedom when it comes time to put the whole thing into some kind of case.
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[ 4.7 ms ] story [ 41.6 ms ] threadHuh, I guess I never really thought about it, but how did they program the first CPUs? Like how did they overcome the chicken/egg situation?
The Rigol deserves a blog post of its own, I've got one too and the better I get in using it the more I'm amazed at what it can do.
I've run into the same 'all you can get is SMD' which is fine for when you're finished but a lot harder while you're still figuring things out. This is where 'proper engineers' can go straight to the finish line and I always struggle.
You also develop some kind of sixth sense for when something is misbehaving. If you haven't read it yet, 'The Soul of a New Machine' might be to your liking.
best of luck with your project!
Oh, and I did read all the way to the end.
Seeing this is just amazing to be honest. Wish you a luck on your project!
Makes doing things larger than 8/16 bit computers very complicated and usually very slow :(
And no shit, Claude has helped with a lot of the EE stuff that I was only semi-knowledgeable about. I want to pursue a multiplier unit using log/anti-log circuits and an LLM suggests multiplying with PWM. For another module I complain about the cost of a 16-bit ADC and the LLM suggests a 12-bit drop-in replacement that costs half as much. I want sine and cosine and the LLM suggests using diodes/resistors to "shape" a voltage to approximate a sine curve—rattles off the resistor values needed.
I breadboard first everything the LLM suggests, dig around on the internet to see if the idea is legit/sound, and in the process have learned an enormous amount about electronics in general.
Nice read, thanks for sharing.