Communication processor and Modbus TCP
13.3 Point-to-point (PtP) communication
S7-1200 Programmable controller
1140 System Manual, V4.2, 09/2016, A5E02486680-AK
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
detection for both devices (Case 1).
● 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 the slaves (Case 1).
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