Siemens Simatic S7-300 CPU 31xC Series User Manual

Configuring
4.11 Planning subnets
S7-300, CPU 31xC and CPU 31x: Installation
4-32 Operating Instructions, Edition 08/2004, A5E00105492-05
Differences in the MPI addresses of CPs/FMs in an S7300 system
Table 4-15 MPI addresses of CPs/FMs in an S7-300 system
Options Example
CP
BUSF
BUSF
DC5V
DC5V
FRCE
FRCE
RUN
RUN
STOP
STOP
CP
CPU
SM
Example:
A system containing an S7-300 CPU and 2
CPs.
You have two options of assigning MPI
addresses to CPs/FMs installed in a system:
CPU CP CP
1st option: The CPU accepts the MPI addresses
you set for the CPs in STEP 7.
MPI addr. MPI
addr.+x
MPI
add.+y
2nd option: The CPU automatically assigns MPI
addresses to the CPs in its system, based on
the following syntax: MPI addr. CPU; MPI
addr.+1; MPI addr.+2.
(Default)
MPI addr. MPI
addr.+1
MPI
addr.+2
Special feature: CPU 315-2 PN/DP and CPU
317
When the central rack of an S7-300 contains
FM/CPs with their own MPI address, the CPU
forms its own communication bus via the
backplane bus for these FM/CPs and separates it
from the other subnets.
The MPI address of those FM/CPs is thus no
longer relevant for the nodes on other subnets.
The MPI address of the CPU is used to
communicate with these FMs/CPs.
Recommended MPI address settings
Reserve MPI address "0" for a service PG, or "1" for a service OP, for temporary
connections of these devices to the subnet. You should therefore assign different MPI
addresses to PGs/OPs operating on the MPI subnet.
Recommended MPI address of the CPU for replacement or service operations:
Reserve MPI address "2" for the CPU. This prevents duplication of MPI addresses after you
connect a CPU with default settings to the MPI subnet (for example, when replacing a CPU).
That is, you should assign an MPI address > "2" to CPUs on the MPI subnet.
Recommended PROFIBUS address settings
Reserve PROFIBUS address "0" for a service PG that you can subsequently connect briefly
to the PROFIBUS subnet as required. You should therefore assign unique PROFIBUS
addresses to PGs integrated in the PROFIBUS subnet.
PROFIBUS DP: Electrical cables or fiber-optic cables?
Use fiber optic cables on a field bus with greater length, rather than copper conductors, in
order to be independent on the transmission rate, and to exclude external interference.

Siemens Simatic S7-300 CPU 31xC Series Specifications

General

Series	S7-300 CPU 31xC
Power Supply	24 V DC
Communication Interfaces	MPI, PROFIBUS DP
Programming Languages	LAD, STL, FBD, SCL
Operating Temperature	0°C to +60°C
Memory	48 KB - 512 KB
Dimensions	40 x 125 x 130 mm (varies by model)