CoCoTANG open-source hardware brings CoCo 3 features to vintage Color Computers

Developer Felipe Antoniosi has released CoCoTANG, an open-source hardware project designed to upgrade vintage Radio Shack Color Computer (CoCo) systems. By utilizing a Sipeed Tang Nano 20K FPGA development board, the project recreates the Graphics, Interrupt, Memory Enhancement (GIME) chip in programmable logic. This allows older CoCo 1 and CoCo 2 machines to access features originally exclusive to the CoCo 3.

The upgrade functions alongside the original Motorola MC6809E processor rather than replacing it with an emulator. It significantly expands system capabilities, including support for up to 8 MB of RAM and enhanced graphics modes. The hardware implementation also introduces modern connectivity, such as HDMI output, to bridge the gap between 1980s computing and contemporary displays.

Technical implementation of CoCoTANG

• FPGA Logic: Uses a Sipeed Tang Nano 20K to implement the GIME chip functionality in programmable logic.
• Memory and Storage: Expands addressable RAM to 8 MB and provides non-volatile storage via a microSD card through a Glenside-compatible IDE interface.
• Video Output: Supports HDMI for modern displays, with configurable analog options including RGB, component, and composite/S-Video.
• Audio Enhancements: Adds stereo sound over HDMI, Orchestra-90 support, and emulation of the Tandy Speech/Sound Cartridge for speech synthesis.
• Hardware Requirements: Requires custom PCB assemblies, including a main board for the CPU/FPGA, PIA adapters, and a replacement address decoder.

Why it matters

This project provides a path for retro-computing enthusiasts to preserve and modernize vintage hardware using open-source schematics and HDL. By releasing the KiCad designs, PCB fabrication files, and FPGA source code on GitHub, the developer enables community-driven hardware maintenance and expansion for the Color Computer ecosystem.