Siemens Simatic S7-300, Hardware And Installation Manual, Page: 143 / 242

Commissioning
S7-300 Programmable Controller Hardware and Installation
A5E00105492-01
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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 PROFIBUS-DP interface. To do so, you
must enable these functions when configuring the CPU as a DP slave in STEP 7.
This is not required for CPU 300 C.
Note
The use of Status and Control function via the PROFIBUS-DP interface extends
the DP cycle.
Data Transfer via Intermediate Memory
CPU 31x-2 DP/31xC-2 DP as DP slave provides an intermediate memory for
PROFIBUS-DP communication. All data exchange between the CPU as DP slave
and the DP master takes place via this intermediate memory. You can configure up
to 32 address areas for this function.
That is, the DP master writes its Data to these intermediate memory address areas
and the CPU reads these data in the user program, and vice versa.
Transfer memory
in the address
area
PROFIBUS
I/Q I/Q
CPU as DP slave
DP master
Figure 8-10 Intermediate memory in CPU 31x-2 DP/31xC-2 DP as DP Slave
Address areas in intermediate memory
In STEP 7, configure the I/O address areas:
•
You can configure up to 32 I/O address areas.
•
Maximum length per address area is 32 bytes.
•
You can configure a maximum of 244 input bytes and 244 outputs bytes.
The table below shows the principle of address areas. You can also find this figure
in the STEP 7 configuration.