Siemens SIMATIC S5 Manual page 179

IM 308-C – addressing, diagnostics and use of the FB IM308C
When is the
control command
valid?
!
9-32
When the control command is issued with the FB IM308C, it takes
approximately one bus cycle (approx. 1 T
calculated by COM ET 200 Windows in bus parameters) before the control
command is broadcast to all DP slaves concerned.
You must use FCT = CC to check whether the control command sent in the
GCGR parameter has already been broadcast to all the DP slaves concerned.
While ERR = DC persists, the inputs affected by the control command
H
cannot be read or the outputs set.
Caution
If you process the inputs or outputs affected by a control command before
the command has been broadcast along the bus to the DP slaves, incorrect
values may be read or set.
Consequently, always check beforehand with FCT = CC to ascertain whether
the control command you sent has already been processed by the DP slaves.
, target rotation time;
TR
ET 200 Distributed I/O System
EWA 4NEB 780 6000-02a