dottech / cscvon8

A crazy small 8-bit CPU built with only seventeen 7400-series chips.

CSCvon8: 8-bit von Neumann Crazy Small CPU

This repository holds the files for my 8-bit "big brother" CPU to the 4-bit Crazy Small CPU. This is a von Neumann style CPU designed with 7400-style logic chips, 32K of RAM, 32K of ROM and a UART. The CPU requires only seventeen chips, not including the clock circuitry. A short video is here.

The overall design of the CPU is covered in Docs/CSCvon8_design.md. Also read the getting started guide and the guide to building the PCB version.

As at the 18th May 2019 I have the CPU running solidly at 3.57MHz on the PCBs that I ordered from the PCB design in the Schematics folder. I've kept a journal with details of my progress from the initial design phase through to the successful build.

The files and folders in this repository are:

• Docs, documents on the design and how to use the tools below
• Examples, example programs for the CPU
• Schematic, a KiCad schematic of the CPU
• cas, the assembler for the CPU
• clc, a very crude compiler that outputs assembly that can be given to cas
• csim, a simulator of the CPU written in Perl
• disasm, a tool to disassemble the instruction ROM contents
• gen_alu, a program to generate the contents of the ALU ROM
• gen_ucode, a program to generate the contents of the Decode ROM
• journal.txt, my running journal of the design and implementation of CSCvon8

There is also a Verilog version with the top-level file being ttlcsvon8.v, the testbench is icarus_tb.v and the Makefile will build and run the Verilog testbench. Some notes on this implementation are in the Docs/implementation_notes.md file.