Siemens SIMATIC S7-300 Series Reference Manual page 95

2.3 CPU 31x-2 as DP Master
Introduction
This section covers the features and technical specifications of the CPU when it is
used as a DP master.
The features and technical specifications of the CPU 31x-2 as the "standard" CPU
are listed in Section 1.
Prerequisite
Should the MPI/DP interface be a DP interface? If so, you must then configure the
interface as a DP interface.
Before the CPU can be put into operation, it must be configured as a DP master.
This means carrying out the following steps in STEP 7 :
S Configure the CPU as a DP master.
S Assign a PROFIBUS address.
S Assign a master diagnostic address.
S Integrate DP slaves into the DP master system.
Is a DP slave a CPU 31x-2?
If so, you will find that DP slave in the PROFIBUS-DP catalog as
"pre-configured station". This DP slave CPU must be assigned a slave
diagnostic address in the DP master. Interconnect the DP master and the DP
slave CPU. Specify the address areas for data exchange with the DP slave
CPU.
Status/Control, Programming via PROFIBUS
As an alternative to the MPI interface, you can program the CPU via
PROFIBUS-DP interface or execute the PG's status and control functions.
Note
The use of Monitor and Modify via the PROFIBUS-DP interface lengthens the DP
cycle.
Equidistance
As of STEP 7 V 5.x you can configure bus cycles of the same length (equidistant)
for PROFIBUS subnets. You can find a detailed description of equidistance in the
STEP 7 online help system.
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
CPU 31x-2 as DP Master/DP Slave and Direct Communication
2-5