Developer built a coding agent, then tested it on a real VT-100 to validate cross-terminal compatibility, fixing flow control, baud limits, Unicode, and OSC sequence bugs.
Key Takeaways
VT-100 uses RS-232 at 9600 baud; MacOS dropped XON/XOFF flow control support, requiring a Linux VM to prevent character drops.
Full-screen redraws at 9600 baud are prohibitively slow; a differential renderer that tracks screen state and makes minimal edits is required.
VT-100 only supports ASCII; Unicode box-drawing characters and spinners must be stripped via an ASCII-only mode.
OSC escape sequences (used for hyperlinks, terminal titles) are not safely ignored by VT-100 and print raw text to screen; a legacy mode suppressing OSCs is necessary.
The ASCII-only mode built for VT-100 compatibility later satisfied an enterprise customer whose modern terminals also lacked Unicode support.
Hacker News Comment Review
Commenters share nostalgia for VT320 and VT520 hardware; one notes the VT520 runs at 115200 baud and remains practical, but modern programs ignoring termcap is a persistent blocker.
MAME emulation of DEC terminals (e.g. vt240) with bitsavers ROM/docs links was offered as a lower-friction path for testing terminal compatibility without hardware.
Notable Comments
@wolvoleo: VT520 reaches 115200 baud and is still usable today, but termcap ignorance in modern software limits it; tmux helps partially.
@chasil: MAME emulates vt240 with bitsavers PDFs and SIMH configs available for software-only terminal compatibility testing.
