Siemens SIMATIC S7-300 Manual page 425

Structure of data record 1
The figure below shows the structure of data record 1 for the parameters of digital output
modules.
You enable a parameter by setting a logic "1" at the corresponding bit of byte 0.
Figure A-2
Note
The "hold last valid value" and "set substitution value" parameters should only be enabled at
byte 0 as an alternative.
S7-300 Automation System Module data
Manual, 08/2006, A5E00105505-04
Data record 1 for parameters of digital output modules
Parameter sets of signal modules
A.3 Parameters of digital output modules
A-5