Siemens Simatic S7-300, Hardware And Installation Manual, Page: 58 / 242

Configuring
S7-300 Programmable Controller Hardware and Installation
4-30
A5E00105492-01
4.10.2 Basics
MPI, PROFIBUS-DP, PtP
Since these subnets are the most commonly used for S7-300 CPUs, we shall take
a closer look at them.
Declaration: Device = Node
In the following, all networked devices are referred to as nodes.
Segment
A segment is a bus link between two terminating resistors. A segment can include
up to 32 nodes. It is also limited by the permissible line length, depending on the
transmission rate.
Transmission rate
These maximum transmission rates are possible:
•
MPI
–
12 Mbps with CPU 318-2 DP
–
187.5 Kbps with all other CPUs
•
PROFIBUS-DP: 12 Mbps
•
PtP:
–
Half duplex: 38.4 Kbps
–
Full duplex: 19.2 Kbps
Number of nodes
Maximum possible number of nodes per subnet:
Table 4-11 Subnet nodes
Parameter MPI PROFIBUS-DP PtP
Number 127 126
1)
2
Addresses 0 to 126 0 to 125 -
Remarks Default: 32 addresses
Reserved are:
•
address 0 for PG
•
address 1 for OP
of those:
•
1 Master (reserved)
•
1 PG connection
(address 0 reserved)
•
124 slaves or other
masters
-
1) Note CPU-specific maximum specifications in the respective CPU manual.
MPI/PROFIBUS-DP addresses
To ensure that all nodes can intercommunicate, you must assign them an address:
•
In the MPI network: an "MPI address"
•
In the PROFIBUS-DP network: a "PROFIBUS-DP address"