Which products are affected?
PROFIBUS communication module with firmware version 1.3
Function description
The EMF 2133IB PROFIBUS communication module is equipped with a monitoring function which monitors the reception of process data telegrams within a specific period of time (watchdog time). This time is transferred to the slave by the Profibus master during the initialisation process.
If the PROFIBUS communication is interrupted permanently, e. g. caused by cable breakage or failure of the PROFIBUS master, no process data is sent to the slave 'DataExchange' state.
When the watchdog time has expired, the response set under code C1882 is executed.
The response of the slave only occurs if:
1. the user has activated the response by selecting 'fault', 'controller inhibit' or 'QSP'.
2. the slave is in the 'DataExchange' state.
3. the user has configured the watchdog time in the master.
If one of these prerequisites is not satisfied the response on the absence of cyclic process data telegrams of the master is not executed.
If the PROFIBUS communication is interrupted for a short period of time only, e. g. caused by a loose contact in the bus cable or at the PROFIBUS plug, this state will also be monitored by means of the newly integrated code C1883. The new code is already active when leaving DataExchange after expiry of the parameterised time (0-65534 ms) thus triggering the response set under code C1882.
A value of 65535 under code C1883 deactivates the monitoring function.
The communication monitoring is described and illustrated in detail in the following:
The master detects the communication fault (loose contact or wire breakage) and puts the slave into the WAIT_PRM state of the DP state machine after only a few microseconds (see diagram below).
Only when the chain of the DP state machine ending the DataExchange (DATA_EXCH) state has been completed, the watchdog time calculated for the slave (in millisecond range) continues to run.
The watchdog time does not continue to run when the slave does not reach the DataExchange state due to repeated communication faults (e. g. cased by loose contact). In this case the monitoring function (C1883) is activated.
Applications
If the PROFIBUS communication is interrupted during the start-up or during operation (loose contact or cable breakage) the drive controller can be driven to a defined state.
