Technical data

Cyclic operation
The cyclic program has the following structure for all stations in the CYCLE
SYNCHRONIZED update mode:
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 GP bytes available to the
PLC before the PLC cycle control point and on the other hand the CP can
only process the GP output byte after output of the PIQ.
If one of the SIMATIC S5 PLCs
fails
, the switch off safety strategy for I/O
signals is used for the "global I/Os". If a PLC stops, all outputs and
therefore all GP output bytes sent by this PLC are set to zero. This means
that these GP bytes are automatically sent to all other receiving stations.
The failure of a complete station (e.g. caused by a power failure) can be
detected by the CP 5430 TF/CP 5431 FMS using ANR 201.
Control program
Cycle
checkpoint
HDB RECEIVE call with
ANR 211
(last statement in cyclic
program before the end
of the block)
Call HDB SEND with
ANR 210
(at the start of the cyclic
program)
Fig. 9.7: Structure of the Cyclic Program for all Stations
Communication with Global I/Os B8976060/01
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