VT220 Serial Console Notes

DB25 → DB9, 9600 8N1, ttyUSB0

A VT220 is just an RS-232 endpoint. The “mystery” is always cable topology or framing. These are my notes from getting it to behave as a Linux serial console.

Setup

• VT220: DB25
• Host: Linux + USB-to-RS-232 (ttyUSB0)
• Default framing I used: 9600 8N1
• Unit: VT220-A2 (white phosphor)

VT220 variants

• Mine: VT220-A2 — white phosphor.
• VT220 shipped with multiple screen/phosphor variants and a large ecosystem of options (keyboards, host modules, serial/printer cabling).

Inside

Signal reality

RS-232 idle sits at negative voltage. If I see 0–3.3V idle, I’m not on RS-232.

Cable topology

Two DTEs → cross TX/RX (null-modem) and share ground.

• DB25 2 → DB9 2
• DB25 3 → DB9 3
• DB25 7 ↔ DB9 5

Framing

Bring-up

I start by proving the adapter and cable with minicom, then switch to getty.

• device: /dev/ttyUSB0
• framing: 9600 8N1
• flow control: off (until I see real overruns)

Getty

I ended up with serial-getty@ttyUSB0 and forced 9600 + TERM=vt220.

Control sequences

These are the ones I actually use when driving the VT220 as a display. ESC means \x1b.

Reset / clear (my default)

• reset attrs: ESC[0m
• normal video: ESC[?5l
• cursor off/on: ESC[?25l / ESC[?25h
• clear screen + home: ESC[2J + ESC[H

This is exactly what ~/Workspace/termino/tools/serial_run.py and serial_panel.py send on startup:

• ESC[0m ESC[?5l ESC[?25l ESC[2J ESC[H

Cursor + line ops

• CUP (cursor position): ESC[{r};{c}H
• EL (erase in line): ESC[K

(See serial_panel.py: it updates only changed lines via CUP+EL.)

SGR (style)

• reset: ESC[0m
• bold: ESC[1m
• underline: ESC[4m
• blink: ESC[5m
• inverse: ESC[7m

Big text (DEC/VT100-style)

• double-height (top/bottom): ESC#3 / ESC#4
• double-width: ESC#6
• normal size: ESC#5

\\x1b[0m\\x1b[2J\\x1b[H

References

• RS-232: RS-232
• Null modem: Null modem
• VT220 manual: EK-VT220-TM-001 (Nov 1984)