The Complete 8 Bit ALU

13 Nov 2016

I finished the ALU (all 8 bits) and the test-board yesterday. It contains 355 transistors without the test board.

In all it took less then two days to construct and trouble-shoot (not including the small boards).

It is interesting to note that the ALU only had one short while the test board had two LED's soldered in backwards and a short.

The back side of the ALU;

The 34 pin connector is wired as below;

The six functions are not encoded so if more then one is selected at a time the functions are calculated and the the results are OR'd together

(I don't think this property has a practical use).

Here is the test-board (just light's and switches);

And finely the block diagram;

Tim

Top Comments

andycrofts over 7 years ago in reply to sek4321 +1

I, years ago worked on a Spectrum Analyzer, using the FFT algorithm. 44-bit microcode instruction word, directly operating shift registers, ALU's etc. Total memory 44-bit by 4-kilobyte Here's a piccie…

andycrofts over 7 years ago in reply to sek4321

I, years ago worked on a Spectrum Analyzer, using the FFT algorithm. 44-bit microcode instruction word, directly operating shift registers, ALU's etc. Total memory 44-bit by 4-kilobyte
Here's a piccie:
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andycrofts over 7 years ago

BIt (no pun intended!) confused.
Trust me, I'm really not being insulting, nor belittling your achievement, BUT:
Y'know, when I read things like Enid Blyton some 50 years ago, I always thought a story had a beginning, middle, and an ending.
The Beginning: Why? What's the purpose/goal? Objective?
The Middle: Design principles, reason for components chosen? Interface to what? (Even a bunch of LED's?)
The End: What I learned, what I'd change, why I didn't just buy a 74LS181 from Farnell?
Good effort in engineering. Yeah, I'm and old git, and I'd probably still make it with a hundred (Russian) ECC83's....
-Andy (making Wireless Sets before Marconi was a twinkle in his Grandfather's eye...) JOKE!
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sek4321 over 7 years ago

This is brilliant! If society as such should break down, after the apocalypse you would actually be able to build a computer on your own :-)

I attached a document describing how to build a 4-bit computer. We use it at the Computer Architecture course here at ICT Engineering.

http://icelab.dk/scratch/minimic.pdf

- Stephan
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timswift over 7 years ago in reply to clem57

The six functions come from 6502 microprocessor the only difference is that on the
6502 the inversion is done outside of the ALU.
after the functions were determined I simply used a MUX to select the proper function and carry out.

Another clever feature of the 6502 is addition and subtraction is always done with the carry in which is set beforehand (if desired).

Tim
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clem57 over 7 years ago

A great job and surprisingly quick too. Where did the design come from?
Clem
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