Industrial Engineer · phase 5 of 16

RS-232 / RS-485

Serial electrical interfaces used for point-to-point or multidrop industrial communication.

The Explain card

Plain English: RS-232 is a point to point serial link between two devices, using a signal referenced to ground. RS-485 is a differential pair that can run a long way and carry many devices on one bus.
Example: A laptop programs an old PLC over RS-232 with a nine pin cable. The same PLC polls a dozen meters across the plant over a single RS-485 pair.
Why it matters: RS-232 is good for a few meters and one partner, RS-485 for over a kilometer and thirty two nodes. Terminating resistors, biasing and which wire is A and which is B are where RS-485 links go wrong.
Hook: One is a handshake, the other is a party line.

How the word is built, where it came from, and what it sits beside in memory.

In a sentence

Connect the PLC programming port to the drive with an RS-232 cable, then match the baud rate, data bits, parity, and stop bits.

Letter by letter

Where it came from

Origin: English standards designation, shortened from Recommended Standard 232 and issued by the Electronic Industries Association
Entered the language: 1960
What changed: The document label became the common name for the interface, while later revisions used designations such as EIA-232 and TIA-232.

How it is spelled

Capitalisation: Write RS in capitals and retain the hyphen before 232, even mid-sentence.
Plural and possessive: Use RS-232 interfaces for the plural and RS-232's pinout for the possessive.
Out loud: Spelled out letter by letter.

Same family

Broken into chunks

What it sits beside

Same subject

Same shape

numbered serial-interface standards

industrial serial-port labels

Phase 5: PLC Industrial Communications

The protocols that let controllers, drives and operator panels talk, plus the addressing and description files that make them agree on what was said.