Rs422 And Rs485 Operating Modes - Siemens SIMATIC S7-1200 System Manual

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Communication processor and Modbus TCP

13.3 Point-to-point (PtP) communication

RS422 and RS485 operating modes

Configuring the RS422

For RS422 mode, there are three operating modes depending on your network configuration.

Select one of these operating modes based on the devices in your network. The different

selections for Receive line initial state reference the cases shown below for more details.

● Full duplex (RS422) four wire mode (point-to-point connection): select this option when

there are two devices on your network. In the Receive line initial state:

– Select none when you supply the bias and termination (Case 3).

– Select forward bias to use internal bias and termination (Case 2).

– Select reverse bias to use internal bias and termination, and enable cable break

● Full duplex (RS422) four wire mode (multipoint master): select this option for the master

device when you have a network with one master and multiple slaves. In the Receive line

initial state:

– Select none when you supply the bias and termination (Case 3).

– Select forward bias to use internal bias and termination (Case 2).

– Cable break detection is not possible in this mode.

● Full duplex (RS422) four wire mode (multipoint slave): Select this option for all the slave

devices when you have a network with one master and multiple slaves. In the Receive

line initial state:

– Select none when you supply the bias and termination (Case 3).

– Select forward bias to use internal bias and termination (Case 2).

– Select reverse bias to use internal bias and termination, and enable cable break

detection for both devices (Case 1).

detection for the slaves (Case 1).

S7-1200 Programmable controller

System Manual, V4.2, 09/2016, A5E02486680-AK