Siemens Simatic S7-300 CPU 31xC Series Installation And Operating Instructions Manual page 153

Programming, status/control via PROFIBUS
As an alternative to the MPI interface, you can program the CPU or execute the PG's status
and control functions via the PROFIBUS­DP interface.
Note
The use of Status and Control function via the PROFIBUS-DP interface extends the DP
cycle.
Data transfer via transfer memory
The DP-CPU operating as a DP slave provides a transfer memory for PROFIBUS DP. All
data exchange between the CPU as DP slave and the DP master takes place via this
transfer memory. You can configure up to 32 address areas for this function.
That is, the DP master writes its data to these transfer memory address areas, the CPU
reads these data in the user program, and vice versa.
Figure 8-1
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05
DP master
Intermediate
memory in
I/O address area
PROFIBUS
Transfer memory in a DP CPU operating as a DP slave
8.5 Commissioning PROFIBUS DP
CPU as DP slave
I/O
I/O
Commissioning
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