Installation
13 (66)
3.4
Serial Subnetwork Interface
Serial Connector
The serial subnetwork is connected via a 9-pin female D-sub connector. The allocation of sig-
nals to the different pins in the connector depends on which physical communication interface
is used (RS-232, RS-422 or RS-485).
9
6
1
5 (female)
Fig. 10
D-sub connector (DE-9F)
Pin
Description
RS-232
RS-422
RS-485
1
+5 V Output (100 mA max.)
x
x
x
2
RS-232 Rx
x
3
RS-232 Tx
x
4
(reserved)
5
Signal Ground
x
x
x
6
RS-422 Rx +
x
7
RS-422 Rx -
x
8
RS-485 + / RS-422 Tx +
x
x
9
RS-485 - / RS-422 Tx -
x
x
Housing
Shield
x
x
x
Do not connect Signal Ground (pin 5) to Protective Earth (PE) of other nodes on
the subnetwork, as this may damage the on-board serial transceivers. Only
connect it to the Signal Ground of the other nodes (if available).
Bias Resistors (RS-485 only)
When idle, RS-485 enters an indeterminate state, which may cause the serial receivers to pick
up noise from the serial lines and interpret this as data. To prevent this, the serial lines should
be forced into a known state using
bias resistors
.
The bias resistors form a voltage divider, forcing the voltage between the differential pair to be
higher than the threshold for the serial receivers, typically >200 mV.
Bias resistors should only be installed on one node. Installing bias resistors on several nodes
may compromise the signal quality on the network and cause transmission problems.
Termination (RS-485 and RS-422 only)
To avoid reflections on the serial lines, it is important to properly terminate the subnetwork by
placing termination resistors between the serial receivers near the end nodes.
The resistor value should ideally match the characteristic impedance of the cable, typically
100–120 Ω.
Anybus
®
Communicator
™
PROFINET
®
IRT (2.32) User Manual
SCM-1202-033-EN 1.1
