Siemens Simatic S7-300 CPU 31xC Series Installation And Operating Instructions Manual page 156

Commissioning
8.5 Commissioning PROFIBUS DP
Working with transfer memory
Note the following rules when working with the transfer memory:
• Assignment of address areas:
• The user can define these addresses. In the user program, access data with load/transfer
• The lowest address of specific address areas is their respective area start address.
• The length, unit and consistency of the address areas for DP master and DP slave must
S5 DP master
If you use an IM 308-C as a DP master and the DP CPU as a DP slave, the following applies
to the exchange of consistent data.
You have to program FB192 in IM 308-C to enable exchange of consistent data between a
DP master and the DP slave. With the FB192, the data of the DP CPU are only output or
read out in a consistent block.
S5-95 as DP master
If you set up an AG S5-95 for operation as DP master, you also have to set its bus
parameters for the DP CPU as DP slave.
Data transfer in STOP mode
The slave DP CPU goes into STOP: Data in the transfer memory of the CPU are overwritten
with "0" value, that is, the DP master reads "0."
The DP master goes into STOP: Current data in the transfer memory of the CPU are
retained and can thus be read by the CPU.
8-32
– Input data of DP slaves are always output data of the DP master
– Output data of DP slaves are always input data of the DP master
instructions or with SFC 14 and SFC 15. You can also define addresses of the process
image of inputs or outputs.
be identical.
Note
Assign addresses from the DP address area of the DP CPU to the transfer memory.
You cannot assign addresses specified for the transfer memory again for the I/O modules
on the DP CPU.
Further information on the use of consistent data areas in transfer memory is found at the
end of this subsection.
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05