Siemens SIMATIC ET 200S Operating Instructions Manual page 219

Note
Only one of the following control bits can be set at a particular time:
LOAD_VAL or LOAD_PREPARE.
Otherwise, the ERR_LOAD error is reported until all the specified control bits are deleted
again.
The ERR_LOAD error bit is only deleted when the following is carried out correctly.
Acknowledgment Principle in Isochronous Mode
In isochronous mode, 4 or 6 bus cycles are required to reset the status bits and to accept
values during the load function in this mode.
Figure 3-43
Technological Functions
Operating Instructions, 06/2010, A5E00124867-07
Acknowledgment Principle in Isochronous Mode
1Count5V
3.9 Position feedback
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