Technical data

8.1.5 Sequence of the Data Transmission
To understand how the services are handled, the following section shows
how a data exchange must be coordinated in the control program
depending on the data transmission service used. It is assumed that the
transmitter and receiver are SIMATIC PLCs which exchange data via the
CP 5430 TF/CP 5431 FMS.
Data are transmitted with the SEND HDB, data and acknowledgments
(confirmation, indication) are received with the RECEIVE HDB. To be able
to monitor the data exchange, you must constantly evaluate the status word
for this job.
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As long as an indication is waiting to be accepted by the
PLC, the corresponding SAP does not have a receive buffer.
Free Layer 2 Communication B8976060/02
Volume 1 8 - 18