Rs-485 Operating Mode; Figure 14: Bus Connection Rs-485 Operating Mode, Half-Duplex - WAGO 750-652/040-000 Manual

WAGO-I/O-SYSTEM 750 XTR
750-652/040-000 Serial Interface RS-232/RS-485 XTR
7.2.3

RS-485 Operating Mode

Figure 14: 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 Ω ... 120 Ω resistor apiece to both bus ends.
For communication between 2 or more 750-652/040-000 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 750-652/040-000 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.
Connect Devices 51
Manual
Version 1.3.0