Siemens Simatic series Manual page 49

Parameter data records
B.2 Structure of the parameter data records DI mode
Structure of a data record in the DI mode
The example in the figure below shows the structure of data record 0 for channel 0. The
structure of channels 1 to 15 is identical. 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-1
48
Structure of data record 0: Bytes 0 to 3
DI 16x24VDC HF Digital Input Module (6ES7521-1BH00-0AB0)
Manual, 08/2018, A5E03485952-AG