B&R Automation PC 3100 User Manual page 65

4.7.4.2.3.4 Operation as RS485 interface
The pins of the RS422 default interface (1, 4, 6 and 9) must be used for operation. To do this, connect the pins
as shown.
The RTS line must be switched by the driver for each transmission or reception; switching back does not take place
automatically. This cannot be configured in Windows.
With long cable lengths, the voltage drop can result in greater potential differences between the bus devices, which
can hinder communication. This can be improved by running the ground wire with the others.
The cable ends of an RS485 bus should be terminated (at least for longer cable lengths or higher transfer rates).
Passive termination can normally be used by connecting the signal lines via a 120 Ω resistor at each of the two
bus ends; see "Terminating resistor" for the IF card.
4.7.4.2.3.5 Terminating resistor
A terminating resistor for the serial interface is already integrated in the IF option. This can be switched on or off
with a switch (1); it is necessary to open the system unit for this. A switched-on terminating resistor is indicated by
a yellow LED (2) (see "Reading LED status indicators" on page
Automation PC 3100 User's manual V 2.10
9
RXD
4
TXD
6
RXD
1
TXD
Figure 1: RS232/RS422/RS485 interface - Operation in RS485 mode
DATA
DATA
241).
Technical data
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