This is a PCB version of Ben Eater’s 8-bit breadboard computer. It’s based on the ‘Simple As Possible’ architecture, with modifications made to make the computer turing complete. My main goal building this was to learn the in’s and out’s of PCB design, but I also learned a whole lot about computer architecture in the process.

The computer is made up of 10 modules and an 8-bit bus.

In the video, the CPU is running a program which increments a counter by 3 and displays it on the output.

I sourced all of the components using Ben Eaters BOM. Not all components were still in stock or even in production anymore, but I match each component as closely as possible. In some cases, I modified the design slightly to accommodate a different component, but each module functions in the same way as Ben Eater computer.

Clock

Clock module with variable frequency and manual mode

Program Counter

4-bit program counter with set, reset, output, and count control signals

Memory Address Register

4-bit register, controlling access to RAM

Registers

3 8-bit registers, for storing, moving, and operating on data

Random Access Memory

16 8-bit memory locations to read and write data to

Arithmetic Logic Unit

Add or subtract 2 8-bit numbers

Control

The decision center of the CPU

Output

A 7-segment display

Bus

8-bit bus and control signals connecting all the modules