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RS232 and RS485 are two ways of connecting industrial devices via cables. RS232 is point-to-point – one device to one other device, over a short distance. RS485 is a bus standard – up to 32 devices sharing the same two-wire cable, over distances up to 1,200 metres. Almost all industrial IoT gateways and routers include RS485 ports.
Modbus RTU and BACnet MS/TP both run over RS485, which is why RS485 is the default field bus for connecting meters, sensors, and controllers to gateways.
- RS232 – point-to-point, max 15 metres, one transmitter and one receiver; used for instrument debug ports and legacy instruments
- RS485 – multi-drop bus, up to 32 devices, max 1,200 m at 100 kbps; carries Modbus RTU and BACnet MS/TP
- ESD protection – industrial RS485 ports include 15 kV ESD protection; important in environments with electrical noise from motors
- Termination – 120 ohm termination resistors required at each end of the RS485 bus for reliable operation