Lenze EPM−T9XX Modular system - Manual (Page 273)

Transmitting parameter data
Consistent parameter data
10
Networking via PROFIBUS−DP
10.5
10.5.4
L
10.5−7 EDSPM−TXXX−9.0−11/2009
10.5.4 Consistent parameter data
In the PROFIBUS communication system, a permanent data exchange takes
place between the master computer (CPU + PROFIBUS master) and the slave.
The PROFIBUS master and the CPU (central processing unit) of the master
computer access a common storage medium for this purpose − the dual port
memory (DPM).
The DPM enables a data exchange into both directions (read/write):
у у
PROFIBUS Master Dual Port Memory (DPM) Central Processing Unit
(CPU)
Without any further data organisation, a slower write action of the PROFIBUS
master might be overtaken by a faster read action of the CPU within a cycle.
To prevent this from happening, the parameter data to be transferred must be
marked as "consistent".
With consistency either "read" or "write" is possible in the data memory if master
and CPU have access at the same time:
l The PROFIBUS master only transfers the data as a complete data record.
l The CPU can only access completely updated data records.
l The PROFIBUS master cannot read or write data as long as the CPU
accesses consistent data.
The result is shown in the following example:
у у
PROFIBUS Master Dual Port Memory (DPM) Central Processing Unit
(CPU)
0 1
0 CPU wants to read!
1
PROFIBUS master wants to write at the same time!
1. Due to the fact that the PROFIBUS master can only write if the CPU does not read, the
PROFIBUS master has to wait until the CPU has read all of the data.
2. The PROFIBUS master only writes complete data records into the DPM.
Consistency is achieved by configuring the PROFIBUS master accordingly. Use
the corresponding instructions of your configuration software for this purpose.
Data communication with
existing consistency
Configuration of consistent data