Siemens SIMATIC ET 200S Operating Instructions Manual page 158

1Count5V/500kHz
3.6 Count Modes
Note
Only one of the following control bits can be set at a particular time:
CMP_VAL1 or CMP_VAL2 or LOAD_VAL or LOAD_PREPARE or C_DOPARAM.
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 Isochrone Mode
In isochrone mode, exactly 4 bus cycles are always required to reset the status bits and to
accept values during the load function.
Figure 3-20
158
Acknowledgment Principle in Isochrone Mode
Technological Functions
Operating Instructions, 02/2007, A5E00124867-05