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Write up of my homebrew CPU build

211 points by wwarren

by P-Nuts

1 subcomments

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.

by jacquesm

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by Taniwha

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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)

by alnwlsn

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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!

by cactacea

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Any time I see rounded corners on a PCB I know someone put love into that board. Well done

by tchanukvadze

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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.

by Mercuriusdream

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Also tried to homebrew CPUs before but couldn't even start due to a wall of things to prepare;
Seeing this is just amazing to be honest. Wish you a luck on your project!

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by artemonster

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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)

by hirvi74

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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."

by komali2

8 subcomments

> 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?

by harmf

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by seedpi

1 subcomments