Siemens SIMATIC ET 200AL, System Manual

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Description
2.1 Introduction to PROFIBUS
PROFIBUS with STEP 7 V13
Function Manual, 12/2014, A5E03775446-AC
15
I/O communication using PROFIBUS DP
Table 2- 1 I/O communication using PROFIBUS DP
Communication between … Explanation
DP master and DP slave
The data exchange between a DP master and DP slaves with I/O modules takes place as
follows: The DP master queries the DP slaves of its master system one after the other,
receives input values from the DP slaves, and transmits output data to the DP slaves
(master-slave principle).
DP master and I-slave A fixed amount of data is transmitted cyclically between the user programs in CPUs of DP
masters and I-slaves.
The DP master does not access the I/O modules of the I-slave, but instead accesses
configured address areas, called transfer areas, that can be inside or outside the process
image of the I-slave CPU. If parts of the process image are used as transfer areas, these
may not be used for actual I/O modules.
Data transmission takes place with load and transfer operations using the process image or
by direct access.
DP master and DP master A fixed amount of data is transmitted cyclically between the user programs in CPUs of DP
masters. A DP/DP coupler is required as additional hardware.
The DP masters mutually access configured address areas, called transfer areas, inside or
outside the process image of the CPUs. If parts of the process image are used as transfer
areas, these may not be used for actual I/O modules.
Data transmission takes place with load and transfer operations using the process image or
by direct access.
Additional information
You can find additional information on the hardware configuration in the STEP 7 online help.