Siemens SIMATIC S7-400H System Manual page 66

Assembly of a CPU 41x–H
5.5 Design and function of the memory cards
Serial number
In version 5 or later, all memory cards have a serial number. This serial number is listed in
INDEX 8 of the SSL Parts List W#16#xy1C. The parts list can be read using SFC 51
"RDSYSST".
You can determine the following when you read the serial number in your user program: The
user program can only be executed when a specific memory card is inserted into the CPU.
This protects against unauthorized copying of the user program, similar to a dongle.
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System Manual, 03/2012, A5E00267695-11
S7-400H