I constructed a prototype on a breadboard just to learn about how the CPU works. It has an 8 bit input, an 8 bit output, 2K ROM and 2K RAM. I wrote a test program that takes two inputs and adds them together.

Here is the YouTube video.

in the video I add 3 and 1, and it outputs 4.
the clock is very slow, only a few Hz. not sure exactly how fast it is.