This repository contains the design for a very low part count 6502 design. It was designed as a hobby project to learn more about writing in assembly language and as a cheap retro computing project. I will upload more design documents, utilities, and general information to this repo as it becomes available.
The full computer fits across two double breadboards. Expensive ICs were removed from the design to bring the cost and size of the project down significantly. A few of the changes are listed below:
- The ROM which usually holds the program was removed; the program is now loaded into and executed from RAM.
- An Arduino Nano writes the assembled program to RAM, generates the 6502's clock, and can print the state of the data bus.
- The 6522 Versatile Interface Adapter was removed and replaced with simple address decoding logic. This makes the project harder to extend.
Below is the memory map for the current design of the computer.
0x0000 - 0x00FF Zero-page general purpose memory
0x0100 - 0x01FF Stack
0x0200 - 0x7FF9 Program memory / General purpose memory
0x7FFA - 0x7FFF Illegal - mirrored vector addresses
0x8000 - 0x8001 Display Data Write
0x8002 - 0xBFFF Unused I/O
0xC000 - 0xFFF9 Illegal - mirrored program addresses
0xFFFA - 0xFFFB Non-maskable Interrupt Vector
0xFFFC - 0xFFFD Reset Vector
0xFFFE - 0xFFFF Interrupt Request/Break Vector
The amazing Ben Eater series on the 6502 inspired this project; it can be found here: https://www.youtube.com/watch?v=LnzuMJLZRdU&list=PLowKtXNTBypFbtuVMUVXNR0z1mu7dp7eH