RS-422

showstack / protocols / rs-422

Also called TIA-422, EIA-422, RS422.

Balanced point-to-point serial signalling with one driver and up to ten receivers. It sits between RS-232 and RS-485: the noise immunity of a differential pair, without the multi-drop arbitration, which suits a one-to-many broadcast rather than a bus.

Device managementPaid specTIAReported

Stewarded by TIA (Telecommunications Industry Association).

Not a traffic flow

An electrical standard, like RS-232 but balanced. The flow is whatever it carries.

What goes wrong

One driver only. RS-422 is not a bus and cannot arbitrate: putting two transmitters on the same pair is an electrical conflict, not a collision that gets retried.

Frequently confused with RS-485 because both are differential pairs at similar voltages. A device wired for one will often part-work with the other, which is worse than not working at all.

Typical use

Machine and deck control in broadcast
Some stage-machinery installations
The physical layer under several proprietary show-control links

Sources

TIA-422-B — Electrical Characteristics of Balanced Voltage Digital Interface Circuits — 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.

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