Siemens SIMATIC FM 458-1 DP User Manual page 123

NOTE
Data transfer
duration
Application Module FM 458-1 DP - User Manual
A5E01078222-02 Edition 03.2009
The old tabular values in the DB should then be overwritten with the
following tabular values. Once this has been completed, at WR_TAB the
REQDB input should be again set from 0 to 1 to activate the next table
sub-set transfer.
This procedure should be repeated until all of the tabular values have
been transferred.
At the last sub-set transfer, input LASTDB of the WR_TAB should be set
from 0 to 1. This signals the SIMATIC FM application module that data
transfer has been completed. The STATUS output of the WR_TAB then
changes from 2 to 0.
If there is adequate user memory available, the table can also be saved
in several different DBs. In this particular case, for each table sub-set
transfer, only the matching DB number at the input DBNUM of the
WR_TAB has to be specified. However, it should be ensured that the
DBs are transferred in the correct sequence, so that all of the tabular
values are transferred in an increasing sequence.
The time taken to transfer the tabular values depends on the following
factors: :
 Number of tabular values
 Size of the data blocks
 Sampling time of the TAB and TAB_D
 WR_TAB processing time
In each cycle, a telegram with 56 tabular values is transferred, from the
control to the SIMATIC FM 458-1 DP application module.
The time taken for a table to be transferred can be calculated as follows:
Duration of the data transfer =
The time taken for the data to be transferred via the P bus is not relevant
for this estimation, as this data transfer time is generally less than 1ms
and generally, the function blocks TAB and TAB_D are configured in
sampling times which are greater than 32ms.
If a table is distributed over several data blocks, the time required
increases. The reason for this is that in addition to the time taken to
transfer the tabular values, which can be determined using the formula
above, the user has to manually make the changes described above.
[No. of tabular values / 56] * cycle time of the
slowest FB
(i.e. TAB, TAB_D or WR_TAB)
Configuring
4-65