8bit homemade CPU out of 74HC logic chips. - Page 1
Forum section: electronics / general

author: PauloConstantino
author_rank: Regular Contributor
timestamp: June 07, 2017, 08:35:50 am
content: Hi, I just wanted to share a video of an 8bit CPU that I have built out of 74HC logic IC's.It pretty much does anything a professional cpu does, just in a more limited and slower way. It's built on breadboards with jumper wires and it works like a charmHere's a video. Schematics are available if you're interested. Schematics attached!

author: The Soulman
author_rank: Super Contributor
timestamp: June 07, 2017, 08:49:48 am
content: How many jumper wires?

author: PauloConstantino
author_rank: Regular Contributor
timestamp: June 07, 2017, 08:56:26 am
content: Didn't count! Probably 500

author: cgroen
author_rank: Unknown
timestamp: June 07, 2017, 09:58:24 am
content: Very nice, and well done keeping track of all the jumper wiresPlease share the schematics, I'm sure other than me would love to see it

author: VK3DRB
author_rank: Super Contributor
timestamp: June 07, 2017, 01:13:33 pm
content: Great job!The breadboards is quite fragile though. Over time, you might get contact problems. You could put it all on a PCB. How far can you go? You could eliminate the 74S181 ALU's and replaced them with discrete logic chips. But replacing the RAM with discrete logic would be going to an extreme.I have considered developing a digital clock using nothing but discrete logic chips. The logic gate outputs light discrete LEDs, so one can see exactly what is going on in the clock.

author: jwm_
author_rank: Frequent Contributor
timestamp: June 07, 2017, 02:47:38 pm
content: I've wanted to do something like this but use a sram as my alu, so it can switch out it's basic operations by rewriting the look up tables depending on what it's doing. Actually, a lot of logic can be replaced with ram lookup tables. Would make for a very reconfigurable CPU.

author: PauloConstantino
author_rank: Regular Contributor
timestamp: June 07, 2017, 07:42:33 pm
content: Quote from: jwm_ on June 07, 2017, 02:47:38 pmNote that its not the alu that makes a cpu reconfigurable. Its the microcode and my cpu is totally reconfigurable via microcode changes. Its not ram but roms that are used to implement function tables. Also rom alus are slower.

author: PauloConstantino
author_rank: Regular Contributor
timestamp: June 07, 2017, 07:48:02 pm
content: Quote from: VK3DRB on June 07, 2017, 01:13:33 pmThis computer is only a prototype. Not made to be permanent. Its impossible to make rams out of chips. They would be too slow. I advise you to do the clock because its a lot of fun!

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: June 08, 2017, 03:06:24 am
content: Quote from: PauloConstantino on June 07, 2017, 07:42:33 pmThere was a time in the late 70's when cpu's with writable control stores were a popular thing in academic circles. Practically every example that I came across that was completed to the running state was based around AMD2900 bit-slice components, which you still can buy. Like the 74181 the AMD2900 chip set was 4 bits wide for the alu and registerfile components. I used to dream about making my own custom machine but the exigencies of regular life and job used up all my time and enthusiasm.

author: yada
author_rank: Frequent Contributor
timestamp: June 08, 2017, 03:32:20 am
content: What does the blue wire next to the red one do? That's crazy.

author: PauloConstantino
author_rank: Regular Contributor
timestamp: June 08, 2017, 11:14:25 am
content: Quote from: yada on June 08, 2017, 03:32:20 amWe having a laugh?

author: amyk
author_rank: Super Contributor
timestamp: June 08, 2017, 11:28:09 am
content: Next step, do it on a PCB. It'll make for some good practice.

author: jonovid
author_rank: Super Contributor
timestamp: June 08, 2017, 11:36:16 am
content: why reinvent the wheelWow! ... because its fun & challenging,go for it

author: PauloConstantino
author_rank: Regular Contributor
timestamp: June 08, 2017, 11:39:54 am
content: Quote from: jonovid on June 08, 2017, 11:36:16 amYou got it Jono.