Data exchange telegram

The data exchange telegram cyclically exchanges data between a master device and the slave devices. The core of the PROFIBUS-DP protocol is a cyclic data exchange in which the master device carries out an I/O data exchange with each slave device within a PROFIBUS-DP cycle. The master device sends values for the outputs to each slave device with a data exchange request telegram. Each slave device responds with values for the inputs in a data exchange response telegram. In this way, all output data and all input data is transmitted with one telegram each. The sequence of the DP modules defined in the DP configuration assigns the output data and the input data to the real process data of the slave devices. The sequence of the I/O data in the data exchange telegram is determined by the sequence in which DP modules are attached to a slave device. During cyclic data exchange, a slave device can send diagnosis messages to the master device. To this end, the slave device sets a flag in the data exchange response telegram, which the master device uses to recognize that the slave device has new diagnostic data. The master device then retrieves this diagnostic data with a SlaveDiag telegram.