The Amethyst retro computer system with color video #VintageComputing #ATmega1284 @txsector

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.


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