Technical data

In cyclic operation, the SEND synchronization point is immediately at the
start of OB 1; the RECEIVE synchronization point at the end of the PLC
cycle. The division into a SEND and a RECEIVE synchronization point is
necessary, since the CP must make the received ZP bytes available to the
PLC before the PLC cycle control point and on the other hand the CP can
only process the ZP output byte after the PIQ has been output.
B8976060/02 Communication with Cyclic I/Os
10 - 15 Volume 1