Question:
Which communication monitoring function is added to the code L-C13881 / L-C14881?
Answer:
The PROFIBUS communication module E94AYCPM monitors the reception of process data telegrams within a certain period of time (watchdog time). This time is transferred to the slave by the profibus master while initialisation is executed. When the PROFIBUS communication is interrupted permanently, e. g. due to cable breakage or failure of the PROFIBUS master, no process data are sent to the slave, which is in status 'DataExchange'. When the watchdog time has expired, the reaction parameterized in code L-C13880 / L-C14880 will be executed.
The precondition for the slave's reaction is that
1. the user has activated the reaction by selecting 'Interference', 'Controller inhibit' or 'QSP'.
2. the slave is in status 'DataExchange'.
3. the user has configured the watchdog time in the master.
If one of these preconditions is not fulfilled, the reaction on the non-reception of cyclic process data telegrams of the master will not be executed.
If there is only a short-term interruption of the PROFIBUS communication. e. g. due to a loose contact in the bus cable or at the PROFIBUS plug, this status will also be monitored with code L-C13881 / L-C14881. This becomes active already when the DataExchange is quit after the parameterized time of (0-65534 ms) has expired. Consequently, the reaction set under code L-C13880 / L-C14880 is activated. A value of 65535 in code L-C13881 / L-C14881 inactivates the monitoring.
The communication monitoring is described schematically:
The master detects the communication interference (loose contact or cable breakage) and puts the slave in the status WAIT_PRM of the DP state machine (see picture on the right) after a few microseconds already. When the DP state machine, which leads to status DataExchange (DATA_EXCH) has been passed, the watchdog time (milliseconds range) calculated for the slave continues to run.
The watchdog time does not continue to run, when in case of repeated communication interference (e. g. loose contact) the slave does not reach the status DataExchange. In this case the monitoring becomes active due to code L-C13881 / L-C14881.
