Lenze E84DGFCR - Manual (Page 61)

EDS84DMOTPNET EN 2.0 - 11/2011
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61
Communication manual 8400 motec PROFINET
Parameter data transfer
Consistent parameter data
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 allows 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 an impermissible status, the transmitted parameter data are to be
marked as "consistent".
Data communication with consistency
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).