8-Bit Breadboard Computer Documentation

Welcome to the documentation of my 8-Bit breadboard computer! Here you will find everything from the overall structure of the build, schematics, explanation of the modules, the instruction set and so much more. Have fun digging into the technical specifications of this project!

//TODO insert image of the finished build here

As the name already tells, this computer is based on an 8-Bit approach, which means that every number that this computer can store or compute arithmetic or logic with is in the range of -128 to 127 or 0 to 255, depending on the interpretation of the number (signed or unsigned). This means that all the registers, the bus, the memory and the ALU are 8-Bit long.
There is one exception: With 8 bits, you wouldn’t be able to write bigger programs, as each program could only use a maximum of 256 bytes. But some instructions are up to three bytes long, and I wanted to have a RAM besides ROM. So I decided to double the addresses bits, resulting in a 16-Bit address. This means that the Program Counter, the Memory Address Register and the Stack Pointer are 16-Bit long. Each of them is split up into a high and a low byte, so addresses can be transferred over the bus in two steps.

Color Coding

The project uses different colors for wires and LEDs. This makes determining the functionality of a cable or the affiliation of an LED to a module much easier, especially during debugging the circuits.

LED/Wire Color	Functionality
220 Ω	4-Bit value
680 Ω	8-Bit value, only for the bus
470 Ω	8-Bit value, everything except the bus
2200 Ω	16-Bit value
	+5V
	GND
	Internal module connections
	CLK + internal module connections*
	Direct connection to the bus
	Control line, connected directly to the controller
	Reset line + direct connection to the bus*

*At some point, I ran out of correct colored wires, that’s why some wire colors are occupied more than once.