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.
Where it sits in the deck
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.
