Matt Sarnoff posts on GitHub details of the Amethyst Colour Video System:
The Amethyst is a retro-styled “home computer” built around an Atmel ATmega1284 microcontroller. It features composite (NTSC) video output with both high-color and high-resolution modes, mono audio output, and a full-travel mechanical keyboard. It includes a full-featured implementation of the powerful Forth programming language, with graphics and sound commands, debugger, and screen editor.
A single USB Type-B cable provides 5V power as well as serial communication with a PC. Amethyst is compatible with the Optiboot (Arduino) bootloader, and new firmware may be uploaded to it without a specialized programming device.
Full specifications
- ATmega1284 microcontroller (8-bit) running at 14.318 MHz
- 16KB internal memory (16352 bytes available for applications)
- 4KB nonvolatile EEPROM memory
- Mechanical keyboard with Cherry MX keyswitches
- NTSC color and monochrome composite video output:
- 256-color, 16-color, and 4-color bitmap graphics at resolutions up to 160×200 pixels
- Monochrome bitmap graphics at resolutions up to 640×200 pixels
- 40×25 and 80×25 monochrome text modes
- 40×25 color text mode
- 40×25 color tiled graphics modes
- Single-channel audio output (pulse wave or PWM)
- USB serial communication at speeds up to 57600 baud
- Four SPI expansion ports for peripherals, controllers, and storage devices
- Only 6 chips (ATmega1284, FT320X, 2x 74HC157, 2x 74HC166)
See the GitHub repo and the video below.