Rs-422 Operating Mode; Figure 15: Bus Connection Rs-422 Operating Mode - WAGO 750-652 Manual

44 Connect Devices
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.
7.2.3

RS-422 Operating Mode

Figure 15: 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 ... 120 Ω resistor apiece to both bus ends.
For communication between 2 or several 750-652 interface modules at low baud
rates or with shorter line lengths, it is not necessary to use the terminal resistors.
If the 750-652 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.
WAGO-I/O-SYSTEM 750
750-652 Serial Interface RS-232 / RS-485
Manual
Version 1.4.0