Biasing And Terminating An Rs485 Network Connector - Siemens S7-1200 System Manual

Hide thumbs Also See for S7-1200:

Table of Contents

Communication processor and Modbus TCP

12.2 Biasing and terminating an RS485 network connector

Biasing and terminating an RS485 network connector

Siemens provides an RS485 network connector (Page 991) that you can use to easily

connect multiple devices to an RS485 network. The connector has two sets of terminals that

allow you to attach the incoming and outgoing network cables. The connector also includes

switches for selectively biasing and terminating the network.

You terminate and bias only the two ends of the RS485 network. The devices in between the

two end devices are not terminated or biased. Bare cable shielding: Approximately 12 mm

(1/2 in) must contact the metal guides of all locations.

Terminating device (bias ON)

The CB 1241 provides internal resistors for terminating and biasing the network. To

terminate and bias the connection, connect TRA to TA and connect TRB to TB to include the

internal resistors to the circuit. CB 1241 does not have a 9-pin connector. The following table

shows the connections to a 9-pin connector on the communications partner.

Switch position = On: Terminated and biased

Switch position = Off: No termination or bias

Switch position = On: Terminated and biased

Termination and bias for the RS485 connector

Network connector

Cable shield

Non-terminating device (bias OFF)

S7-1200 Programmable controller

System Manual, 03/2014, A5E02486680-AG