50 Connect Devices
WAGO-I/O-SYSTEM 750 XTR
750-652/040-000 Serial Interface RS-232/RS-485 XTR
Manual
Version 1.3.0
7.2.2
RS-422 Operating Mode
Figure 13: Bus Connection RS-422 Operating Mode
For the RS-422 operating mode (point-to-point connection), the bus ends (at least
for longer line lengths and greater baud rates) should be terminated with a terminal
resistor.
Generally a passive resistance is used by connecting the signal lines via one
100
Ω
...
120 Ω resistor a
piece to both bus ends.
For communication between 2 or several 750-652/040-000 interface modules at
low baud rates or with shorter line lengths, it is not necessary to use the terminal
resistors.
If the 750-652/040-000 serial interface module works on a network with other
communication partners, the wiring of a resistance-biasing network (known as a
fail-safe network) to one line end can be necessary.
Biasing network
Check the necessity of an external biasing network before start-up.
In modern devices with RS-485/RS-422 interface, this network is either already
integrated or the devices have an improved RS-485/RS-422 receiver. The output
of this receiver is in a defined state if the data line is short-circuited or not active.
