Siemens SIMATIC ET 200SP System Manual page 103

Hardware identifier
In addition to the I/O addresses, STEP 7 automatically assigns a hardware identifier which is
used to identify the modules. A hardware identifier is also assigned to submodules.
The hardware identifier consists of an integer. It is output by the system with diagnostics
alarms. The hardware identifier identifies the faulty module or the functional unit.
Figure 6-6
You also use the hardware identifier for a series of instructions to identify the corresponding
module for the particular instruction.
STEP 7 assigns the hardware identifier and the name of the hardware identifier
automatically. It cannot be changed by the user. STEP 7 assigns the hardware identifier
when you insert components in the device view or network view. The "System constants" tab
includes all hardware identifiers and their names for the selected module.
Figure 6-7
You will find the hardware identifiers and names of all modules in the "Default tag table" of
the PLC tags. The entries in the "Default tag table" of the PLC tags cannot be changed
either.
Distributed I/O system
System Manual, 12/2015, A5E03576849-AF
Example of a hardware identifier from STEP 7
Example of an excerpt from a default tag table in STEP 7
Configuring
6.2 Configuring the CPU
103