Siemens Simatic S7-300 CPU 31xC Series User Manual

Configuring
4.11 Planning subnets
S7-300, CPU 31xC and CPU 31x: Installation
4-42 Operating Instructions, Edition 08/2004, A5E00105492-05
Example: Terminating resistor in the MPI subnet
The figure below shows you an example of an MPI subnet and where to enable the
terminating resistor.
The figure below illustrates where the terminating resistors must be enabled in an MPI
subnet. In this example, the programming device is connected via a stub cable only for the
duration of commissioning or maintenance.
OP 27
PG
PG
RS 485-
Repeater
CPU
PS
ET 200 M
S7-300
CPU
PS
CPU
CPU
PS
ET 200 M
S7-300
CPU
PS
CPU
CPU
PS
ET 200 M
S7-300
CPU
PS
CPU
OP 27
CPU
PS
ET 200 M
S7-300
CPU
PS
CPU
21
21
22
21
21
Key to numbers in the figure
(1) Terminating resistor enabled.
(2) PG connected by means of a stub cable for maintenance purposes
Warning
Disturbance of data traffic might occur on the bus. A bus segment must always be
terminated at both ends with the terminating resistor. This, for example, is not the case if the
last slave with bus connector is off power. The bus connector draws its power from the
station, and the terminating resistor is thus disabled. Please make sure that power is always
supplied to stations on which the terminating resistor is active. Alternatively, you can also
use the PROFIBUS terminator as active bus termination.

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)