Lenze E94AYCPM - Manual (Page 76)

9 Parameter data transfer
9.4 Consistent parameter data
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Lenze · E94AYCPM communication module (PROFIBUS®) · Communication Manual · DMS 12.0 EN · 11/2012 · TD17
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9.4 Consistent parameter data
In the PROFIBUS communication system, data are permanently exchanged between the host (CPU +
PROFIBUS master) and the standard device via the plugged-on communication module. Both the
PROFIBUS master and the CPU (central processing unit) of the host access a joint memory: the dual
port memory (DPM).
The DPM permits a data exchange in both directions (write/read):
It could happen that a slower PROFIBUS master writing would be overtaken by a faster CPU reading
within a cycle time without any further data organisation.
In order to avoid such an impermissible state, the parameter data to be transmitted must be marked
as "consistent".
Data communication with consistent data
With consistency, either "reading" or "writing" is possible when the master and the CPU
simultaneously access the memory:
• The PROFIBUS master transfers data only as a complete data set.
• The CPU can only access completely updated data sets.
• The PROFIBUS master cannot read or write data as long as the CPU accesses consistent data.
The result becomes clear from the example below:
1. As the master can only write if the CPU does not read, the master waits until the data are read
completely by the CPU.
2. The master only writes a complete data set into DPM.
Configuring consistent data
Central processing unit
(CPU)
Dual port memory
(DPM)
PROFIBUS master
CPU wants to read! Master wants to write simultaneously!
Central processing unit
(CPU)
Dual port memory
(DPM)
PROFIBUS master

Note!
Consistency is achieved by an appropriate PROFIBUS master configuration.
For this purpose, refer to the documentation for your configuring software.