-
14
-
4.2.1
Diagnosis during cyclic data transfer
During cyclic data exchange, a slave can report a diagnosis to the master. In this case, the slave sets a flag
in the DataExchange response telegram; whereupon the master recognizes that the slave has new
diagnostics data, which he then picks up with the SlaveDiag telegram. The diagnostic data is therefore not in
real time with the cyclic IO data in the controller, but at least one DP cycle later.
4.3 Synchronization of sync and freeze
With the sync and freeze commands in the GlobalControl request telegram (broadcast telegram), the master
can synchronize the output of the outputs (sync) or the input of the inputs (freeze) for several slaves. When
the sync command is used, the slaves are first switched to the sync mode (acknowledged in the diagnostics
data), then the IO data is exchanged sequentially with the slaves via the DataExchange telegram, a
transmission of the sync command in the GlobalControl telegram then results in the slaves outputting the last
received outputs.
In freeze mode, a freeze command is first sent in the GlobalControl telegram, whereupon all slaves take over
the signals at their inputs and are then sequentially requested by the master with the DataExchange
telegram.
4.4 State of things within the master
The master distinguishes the status CLEAR (all outputs on the Fail_Safe value) and OPERATE (all outputs
have the process value). Typically, the master is switched to the CLEAR mode when e.g. the PLC goes to
STOP.
