Pg Connected To An Ungrounded S7-300 - Siemens S7-300 Installation Manual

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If there is no stationary PG, we recommend:
To connect it to an MPI subnet with "unknown" node addresses, set the following
addresses on the service PG:
• MPI address: 0
• Highest MPI address: 126.
Using 67(3 , you then determine the highest MPI address in the MPI subnet and
adapt the highest MPI address in the PG to that of the MPI subnet.
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Always connect an ungrounded PG to ungrounded MPI subnet nodes or S7-300
PLCs.
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You want to operate with ungrounded nodes. If the MPI at the PG is grounded, you
must interconnect the nodes and the PG with an RS485 repeater. You must
connect the ungrounded nodes to bus segment 2 if the PG is connected to bus
segment 1 (connections A1 B1), or the PG/OP interface.
The figure below shows an RS485 repeater as interface between grounded and
ungrounded nodes of an MPI subnet.
PS
Figure 9-6 PG connected to an ungrounded S7-300
S7-300 Automation System, Hardware and Installation: CPU 312IFM - 318-2 DP
A5E00203919-01
CPU
Bus segment 2
(signals ungrounded)
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PG
Bus segment 1
(signals grounded)
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