RS 485 Repeater
7-4
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
7.3 RS 485 Repeater in Ungrounded and
Grounded Operation
Grounded or ungrounded
The RS 485 repeater is ...
• Grounded, if all other nodes in the segment are also operated with a grounded
potential
• Ungrounded, if all other nodes in the segment are operated with an ungrounded
potential
Note
The bus segment 1 is grounded if you connect a programming device to the
PG/OP socket of the RS 485 repeater. Ground connection is effected since the
MPI in the programming device is grounded and the PG/OP socket is connected
internally with bus segment 1 in the RS 485 repeater.
Grounded operation of the RS 485 repeater
For grounded operation of the RS 485 repeater, you must jump terminals “M” and
“PE” on the top of the RS 485 repeater.
Ungrounded operation of the RS 485 repeater
For ungrounded operation of the RS 485 repeater, “M” and “PE” on the top of the
RS 485 repeater must not be interconnected. In addition, the supply voltage of the
RS 485 repeater must be ungrounded.
Terminal connection diagram
In the case of a repeater configuration with ungrounded reference potential
(ungrounded operation), any interference currents and static charges are
discharged by means of an RC network integrated in the repeater (refer to
Figure 7-1) to the protective conductor.
24 VDC
L+ M PE M 5.2
A1 B1 A1 B1
M
22 nF 10 MΩ
Ground bus
PE
Figure 7-1 RC Network with 10 MΩ for Configuration with Ungrounded Reference
Potential
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