EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: PauloConstantino on June 07, 2017, 08:35:50 am
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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 charm :)
Here's a video. Schematics are available if you're interested. Schematics attached!
https://www.youtube.com/watch?v=017jg0eoO_A (https://www.youtube.com/watch?v=017jg0eoO_A)
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:-+
How many jumper wires?
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Didn't count! Probably 500
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Very nice, and well done keeping track of all the jumper wires :-+
Please share the schematics, I'm sure other than me would love to see it :)
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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.
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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.
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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.
Note 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.
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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.
This 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!
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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.
Note 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.
There 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.
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What does the blue wire next to the red one do? That's crazy.
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What does the blue wire next to the red one do? That's crazy.
We having a laugh? :D
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Next step, do it on a PCB. It'll make for some good practice.
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why reinvent the wheel ::) Wow! ... because its fun & challenging, :-+ :-+ go for it
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why reinvent the wheel ::) Wow! ... because its fun & challenging, :-+ :-+ go for it
You got it Jono.