Lenze · Inverter Drive 8400 motec (PROFINET® option) · DMS 5.0 EN · 02/2019 · TD23
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9
Parameter data transfer
9.5
Consistent parameter data
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9.5
Consistent parameter data
In the PROFINET communication system, data are permanently exchanged between the host (CPU +
I/O controller) and the standard device via the plugged-on I/O device interface module. The I/O
controller 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 I/O controller 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 I/O controller and the CPU
simultaneously access the memory:
• The I/O controller transfers data only as a complete data set.
• The CPU can only access completely updated data sets.
• The I/O controller cannot read or write data as long as the CPU accesses consistent data.
The result becomes clear from the example below:
1. As the I/O controller can only write when the CPU does not read, the I/O controller has to wait
until the data are completely read by the CPU.
2. The I/O controller only writes a complete data set into the DPM.
Configuring consistent data
Central processing unit
(CPU)
Dual port memory
(DPM)
I/O controller
CPU wants to read.
I/O controller wants to write at the same
time.
Central processing unit
(CPU)
Dual port memory
(DPM)
I/O controller
Note!
Consistency is achieved by an appropriate I/O controller configuration (see
documentation for the configuring software).
