Siemens SIMATIC S7-400 Reference Manual page 327

Rules for connection
When you connect a central rack to expansion racks, you must observe the following rules:
● You can connect up to 21 ERs of the S7-400 to one CR.
● The ERs are assigned numbers to identify them. The rack number must be set on the coding
switch of the receive IM. Any rack number between 1 and 21 may be assigned. Numbers
must not be duplicated.
● You may insert up to six send IMs in one CR. However, only two send IMs with 5 V transfer
are allowed in one CR.
● Each line connected to the interface of a send IM can comprise up to four ERs (without 5
V transfer) or one ER (with 5 V transfer).
● The exchange of data via the communication bus is limited to 7 racks, meaning the CR and
ER numbers 1 to 6.
● The maximum (total) cable lengths specified for the type of connection must not be
exceeded.
Table 6-3
Local connection with 5 V transfer via IM 460-1 and IM 461-1
Local connection without 5 V transfer via IM 460-0 and IM 461-0
Remote connection via IM 460-3 and IM 461-3
Remote connection via IM 460-4 and IM 461-4
Terminator
The bus must be terminated in the last EU of a line. To do this, plug in the appropriate terminator
in the lower front connector of the receive IM in the last EU of the line. Unused front connectors
in a send IM do not have to be terminated. The IM 461-1 does not require a terminator.
Table 6-4
IM 461-0
IM 461-3
IM 461-4
The following figure shows you a typical configuration with send IMs, receive IMs and
terminators.
S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08
Cable for different connections
Connection type
Terminators for the Receive IMs
Receive IM
6.1 Common features of the interface modules
Terminator
6ES7461-0AA00-7AA0
6ES7461-3AA00-7AA0
6ES7461-4AA00-7AA0
Interface modules
Maximum (total) line
length
1.5 m
5 m
102.25 m
605 m
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