RS-232

showstack / protocols / rs-232

Also called TIA-232, EIA-232, RS232, Serial.

Single-ended point-to-point serial signalling, and still the control input on a large amount of installed projection, switching and audio gear. One driver, one receiver, one cable, no addressing — which is exactly why it keeps working long after the network around it has been replaced.

Device managementPaid specTIAReported

Stewarded by TIA (Telecommunications Industry Association).

Not a traffic flow

An electrical and connector standard. What rides on it decides the flow.

What goes wrong

Single-ended and unbalanced: the signal is referenced to ground, so it has none of the noise rejection of RS-422 or RS-485 and is limited to short runs. It also means a ground difference between the two ends becomes part of the signal.

Straight-through versus null-modem is still the first thing to check. Two devices that both expect to be the DTE need their transmit and receive swapped, and nothing about the connector tells you which is which.

Flow control is often the difference between working and not. A device expecting hardware handshaking on a cable that carries only three wires will accept the first command and then go quiet.

Baud, data bits, parity and stop bits all have to match at both ends, and a mismatch produces plausible-looking garbage rather than silence.

Typical use

Projector and display control
Matrix switchers and older audio processors
Serial passthrough in control systems and HDBaseT extenders

Sources

TIA-232-F — Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange — Telecommunications Industry Association primary

Understand the mechanism

Robots, animatronics and connected things How software talks to software

Something wrong, or missing?

Known gaps on this entry: default_ports, first_published, implementations. If you can source one of them, that is a ten minute pull request.

Edit this entry on GitHub — one file, editable in your browser, and your handle goes on it permanently.

Work at TIA (Telecommunications Industry Association)? Confirm or correct this entry — it is free, it stays free, and nothing about it is for sale.