Designing and Building an 8-Bit Game Console From the GND Up

The long period of sheltering at home may at least offer some time to set aside for personal projects, and one engineer, Clyde Shaffer took advantage to delve into one: designing and building his own 8-bit game console. The system is based around a 6502 CPU and, while it is still experimental and has glitches to work out, video, sound, and input are functional to some extent, as can be seen in the project’s May 2020 update. Peripheral boards for the console are implemented with basic 74HC logic.

Currently, the project features a graphics board with a fast sprite copy functionality, which allows images from a pre-loaded buffer to be drawn to the screen independently of the CPU and, in fact, much more quickly than if the CPU tried to copy these bytes in software. Other features of the hardware include basic transparency, transparent pixels that enable the background to show behind sprites as they move around the screen.

For ease of testing new versions of the project’s software, prototypes use an adaptor board so EEPROM chips can be swapped quickly. The plan for the final version is to store finished programs on fixed cartridges with custom plastic shells. Another development tool being implemented is an emulator designed so software versions can be tested without burning programs to the ROM chip. Currently, the emulator only simulates the graphics card and CPU.

Examples of major glitches encountered include a memory access problem that occurs when the CPU accesses Graphics or Video RAM directly. While the upper half of the memory banks work well, the lower half becomes distorted. However, the graphics card works without issue if an Arduino is used to emulate the motherboard.

Shaffer intends to document this full process on his site by creating logs and maintaining a roadmap. There you will be able to find the project’s goals, target specs, and any self-imposed rules, as well as concepts, design, and testing for all elements of the console. Shaffer has plans in motion for graphics/video, audio, a cartridge system, which will include programming ROMs, controller inputs, software, and overall design.