Technical data

WAGO-I/O-SYSTEM 750 Connect Devices 45
750-652 Serial Interface RS-232 / RS-485
Manual
Version 1.3.0
7.2.2 RS-485 Operating Mode
Figure 13: Bus Connection RS-485 Operating Mode, Half-Duplex
In the RS-485 operating mode (bus connection), a twisted-pair cable should be
used at least for larger cable lengths or higher transmission rates. The ends of the
cable 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 more 750-652 interface modules at low baud
rates or with shorter line lengths, it is not necessary to use the terminal resistors.
The receiver built into the I/O module has a defined output state if both inputs are
not connected and the data line has a short circuit or no transmitter is active (idle
line).
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.