Siemens simatic c7-621 Hardware Installation Manual page 70

Connecting a Programming Device / PC to a C7
Attaching a If you install the nodes of a subnet or an S7-300 without grounding, only an
Programming
ungrounded programming device can be connected to the subnet or to the
Device to an
S7-300.
Ungrounded Node
Connecting a
You want to use ungrounded nodes. If the MPI is grounded on the PG, you
Grounded
must include an RS 485 repeater between the nodes and the PG. The
Programming ungrounded nodes must be connected to bus segment 2 if the PG is connected
Device to the MPI to bus segment 1 (terminals A1 B1) or the programming device/OP interface
(see Chapter 7 in the reference manual Module Data).
Figure 4-4 shows the RS 485 repeater as an interface between a grounded and
an ungrounded node in an MPI subnet.
Figure 4-4
4-6
C7
Bus segment 2
signals ungrounded
PG Connected to an Ungrounded S7-300
Bus segment 1
signals grounded
PG
C7-621 / C7-621 AS-i Control Systems
C79000-G7076-C621-01