Please note that slave data can be overwritten with zeros in case of a DP slave failure.

Such failures can lead to zeros or no values in the data flow, even for a few milliseconds. In real time automation systems this effect may cause failures of the entire system which are hard to examine.

Concerning incoming data (master's view), there are some possibilities using the DP monitoring functions of the S7-system, such as alert function blocks.

When it comes to outgoing data the receiving systems, which are connected to the PROFIBUS via ibaBM-DP and interface boards like ibaLink-VME or ibaLink-SM-64-io, can only read 32 analog and 32 digital data per slave (= module in ibaPDA) from the iba interface cards.

On that end even the breakdown of the entire DP line cannot be detected. In case of a PROFIBUS failure the most recent signal values remain.

Note

There is a way to realize corresponding indications by using the data set. For example a digital channel of this data set can serve as a "hot wire". The master should hold this digital value always on TRUE (= 1) as long as the PROFIBUS works properly. In case of a short DP failure the master will write zero to all outgoing data for a short time, including the digital monitoring signal. When the receiving system reads a FALSE (= 0) on the digital channel it is clear that all other values are not valid and therefore should not be taken into account.

Other methods may be engineered as well by means of the data set. Particularly a dynamic life sign, i. e. a toggling digital signal, from the master is recommended.