Siemens Simatic series Manual page 51

Parameter data records
B.3 Structure of the parameter data records Counting mode
Structure of data record 0 of the Counting mode
The example in the figure below shows the structure of data record 0 for channel 0. The
structure of channel 1 is identical, the values are located in data record 1.
The values in byte 0 and byte 1 are fixed and may not be changed.
Enable a parameter by setting the corresponding bit to "1".
Figure B-2 Structure of data record 0: Bytes 0 to 4
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DI 16x24VDC HF Digital Input Module (6ES7521-1BH00-0AB0)
Manual, 08/2018, A5E03485952-AG