Configuring Hardware and Communication Connections STEP 7.pdf

Settings at the DP Slave (DP Interface Module)
Configuring the Distributed I/O (DP)
Isochrone input and output modules have to be made known to the DR interface
modules (i.e. IM 151-1 High Feature) as isochrone components. To do so, proceed
as follows:
1. Double-click the icon for the DP slave (i.e. IM 151-1 High Feature).
2. In the "Properties - DP Slave" dialog box, select the "Isochrone Mode" tab and
make the following settings:
- Select the "Synchronize DP slave to constant bus cycle time for DP
cycle…" check box.
- Select the modules desired for "isochrone operation." Modules that do not
support isochrone mode or for which this option was not selected will not
be included in a calculation of the Ti (read in process values) times and the
To (output process values) times.
3. Confirm your entries and close the dialog box by clicking "OK".
After this, a message will appear to remind you that the Ti and To times in the
configuration of the DP master system are not yet updated.
Updating the Times (Ti, To and the lag time)
To update the Ti and To times, go to the "Options" dialog box and select the
"Constant Bus Cycle Time" tab, as previously described in the section "Settings at
the DP Master System". Then click the "Recalculate" button.
The calculation process will enter a cycle time in the "Constant DP Cycle" field.
This cycle time is one that will ensure adherence to the DP cycle time even in the
case of strong interference (i.e. EMC related disturbances). Under very stable
conditions, this value can be reduced down to the minimum value. The system
requires that new values be changed in terms of the specified interval. For this
reason, use a stepping switch to change this value. A greater DP cycle time may
be necessary to ensure that OB6x has enough calculation time available to it.
During automatic calculation, the values for Ti and To are set to their minimum
values. These values can also be changed and set within the limits shown. The
maximum values for Ti and To can be extended by setting a greater constant DP
cycle time.
To update the lag time between the global control frame and the call of the
synchronous cycle interrupt OB, open the properties sheet for the CPU, select the
"Synchronous Cycle Interrupts" tab and then click the "Default" button to have the
value recalculated. In some isolated cases, it may be necessary to move up the
start of OB6x. In this case, correct the calculated value manually. The value
entered is understood to be in milliseconds.
Configuring Hardware and Communication Connections with STEP 7
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