Beckhoff EL6731 Documentation page 116

Parameterization and commissioning
Effect on the DP connection (NoAnswer reaction) if the slave either does not answer or does not
answer correctly
This specifies whether the DP connection to the slave should be removed immediately in the absence of a
correct reception telegram, or only after the DP watchdog time has elapsed (see the slave's Profibus [} 96]
tab).
1. If the DP connection is to be removed immediately (Leave Data Exch, default setting) the slave is re-
moved from the polling list and is no longer addressed in the following DP cycles until the DP connec-
tion is established once again. In order to re-establish the DP connection to the slave, at least 7 tele-
grams are sent, and the process generally requires at least 10-20 ms.
2. If the DP connection is only to be removed when the slave has not answered (or not answered cor-
rectly) within the DP watchdog time (Stay in Data-Exch (for WD-Time)), a further attempt is made in
the next polling cycle to address the slave, but if the slave does not answer, a repeat is not sent.
The "Stay in Data-Exch (for WD-Time))" (2.) setting makes sense if the PROFIBUS cycle is to continue to
operate at the most regular possible period even if a slave fails, and if the failure of a slave for one or more
cycles can be tolerated (e.g. in the DP/MC (Equidistant) [} 40] operation mode). In this case the DP
watchdog time for the slave should be set according to the tolerable outage time of the slave, and the Max
Retry Limit (DX) (see Bus parameters [} 87] dialog) should be set to 0.
Normal DP cycle (12 Mbaud, 5 slaves, an average of 20 bytes I, 20 bytes O for each slave) in the "Stay
in Data-Exch (for WD-Time)" mode
Fig. 118: Diagram showing a normal DP cycle
First faulty and subsequent DP cycles in the "Stay in Data-Exch (for WD-Time)" mode (slave 3 does
not respond)
Fig. 119: Diagram: First faulty and subsequent DP cycles in the "Stay in Data-Exch (for WD-Time)" mode
Changes of the slave's input data if the slave does not respond correctly
This specifies whether the slave's input data is set to 0 when it fails ("Inputs will be set to 0", which is the
default setting) or whether the existing values are retained ("No changes"). In either case the DpState [} 121]
of the slave is set to value other than 0, so that the task can always recognize whether or not the data is
valid. If a slave gives a faulty answer, the input data is always set to 0, independently of the setting of
Changes of the Input Data.
Setting the slave's restart behavior if the DP connection to the slave is removed
This specifies whether the DP connection to slave whose DP connection has been removed is automatically
re-established, or whether this should be done manually as a result of a call to ADS-WriteControl (see ADS-
Interface [} 42]).
116 Version: 2.8 EL6731