Siemens S7-1200 System Manual page 725

The two wires at the opposite end of
the RS485 cable must be inserted into
the MM4 drive terminal blocks. To
make the cable connection on a MM4
drive, remove the drive cover(s) to
access the terminal blocks. See the
MM4 user manual for details about
how to remove the covers(s) of your
specific drive.
The terminal block connections are labeled numerically. Using a PROFIBUS connector on
the S7-1200 side, connect the A terminal of the cable to the drive terminal 15 (for an MM420)
or terminal 30 (MM440). Connect the B terminal of B (P) A (N) the cable connector to
terminal 14 (MM420) or terminal 29 (MM440).
If the S7-1200 is a terminating node in the network, or if the connection is point-to-point, it is
necessary to use terminals A1 and B1 (not A2 and B2) of the connector since they allow the
termination settings to be set (for example, with DP connector type 6ES7 972--0BA40--
0X40).
Replace drive covers properly before supplying power
Make sure the drive covers are replaced properly before supplying power to the unit.
If the drive is configured as the terminating
node in the network, then termination and
bias resistors must also be wired to the
appropriate terminal connections. This
diagram shows examples of the MM4 drive
connections necessary for termination and
bias.
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
CAUTION
Communication processor and Modbus TCP
12.4 Universal serial interface (USS) communication
725