Siemens SIMATIC S7-300 Manual page 30

Communication with the S7-300
5.1 Interfaces
5.1.2 MPI/DP interface (X1)
Availability
The Technology CPU features an MPI/DP interface (X1). A CPU with MPI/DP interface is
supplied with default MPI parameter settings. Depending on your requirements, you may
need to reconfigure the interface as a DP interface in STEP 7.
MPI properties
The MPI (Multi-Point Interface) represents the CPU interface for PG/OP connections, or for
communication on an MPI subnet.
The typical (default) transmission rate of all CPUs is 187.5 kbaud. You can also set 19.2
kbps for communication with an S7-200. You can set baud rates of up to 12 Mbaud.
The CPU automatically broadcasts its bus configuration via the MPI interface (the
transmission rate, for example). A PG, for example, can thus receive the correct parameters
and automatically connect to a MPI subnet.
Note
You may only connect PGs to an MPI subnet which is in RUN.
Other stations (for example, OP, TD, ...) should not be connected to the MPI subnet while
the system is in RUN. Otherwise, transferred data might be corrupted as a result
interference, or global data packages may be lost.
Note
Before you transfer data to the CPU via the MPI interface, you should increase the baud rate
to 1.5 Mbaud or else the data transmission can take a very long time (up to 15 minutes at
187.5 kbaud)!
Operating modes of the MPI/DP interface
Operating modes for MPI/DP interface (X1):
• MPI
• DP master
• DP slave
• I slave
5-2
S7-300 CPU Data: CPU 315T-2 DP
Manual, 12/2005, A5E00427933-02