4-bit Homebrew CPU - counting test

This is an extremely primitive CPU I've been stressing over for the past week or so. It operates on 4 bits at a time, but the accumulator, program counter and Index registers are all 16-bit.

It is running a simple increment program to make sure the accumulator and addition logic are sane. It works by shifting the accumulator through the addition Finite State Machine.

There are two blown segments on the LED display. I'm aware my desk is a mess.

I am now calling this processor CADET, after the IBM 1620 which used lookup tables to do arithmetic (same as my machine). It stands for, "Can't Add, Doesn't Even Try."

http://kaput.retroarchive.org/CADET/

Category:

Science & Technology

Tags:

• homebrew
• cpu
• computer
• 4-bit
• ttl
• discrete

[buzbee1]

Nicely done. How about a link to schematics and more detail?

[256byteram]

@buzbee1 yes, there's a link in the description now.

[Desmaad]

What was that crackling sound I heard at the beginning of the 1KHz segment?

[256byteram]

@Desmaad Probably me connecting the mains to the ATX power supply

[ravingidiot]

Using a LUT for performing addition is a nifty design decision hadn't considered. What influenced your decision to use this implementation?

[dosgamer74]

That's a remarkably-low discrete TTL chip count, given that it contains 16-bit wide CPU registers :-) Awesome work!

[vk2zay]

Awesome. Trust me, your desk is not a mess!

[LunaVorax]

This really is awesome, but what is the use of it?

[Dropshock0]

@Esperantanaso He said in the description that there are two blown segments on the LED display.

[Esperantanaso]

That is a neat idea to make a 4 bit computer operate on a large amount of RAM. Why were some of the segments in the display not lit for certain numbers?