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Appendix L — AVR for retro computing

Purpose

Apply AVR fundamentals to useful interfaces around older computers without hiding the electrical/protocol boundaries.

Candidate projects

  • TTL serial adapter/bridge;
  • dual-UART bridge;
  • terminal or BBS-side controller;
  • baud/protocol diagnostic tool;
  • simple GPIO/joystick-style interface where electrically appropriate;
  • serial-to-modern-host gateway component.

Serial bridge progression

Start with polling UART echo, then buffering/interrupts, then dual-UART forwarding. The existing EduAVR dual-UART examples provide a foundation.

Electrical boundary

Never equate TTL UART with RS-232. Use the correct transceiver and connector convention. Verify voltage levels and grounding before connecting vintage equipment.

Protocol boundary

Separate byte transport from higher-level protocol. A correct UART configuration does not imply that terminal control, file transfer or application framing is correct.

Design principle

Make adapters reversible and observable: labelled connectors, test points, documented pinouts and no unexplained level conversion.

Project idea

Build a small serial diagnostic/bridge tool that reports framing/configuration, forwards data and exposes counters for errors/traffic.