Siemens SIMATIC ET 200S Manual page 78

Configuration Options
3.8 Option handling
Features
Option handling enables you to set up the ET 200S for future expansions (options).
Option handling means that you install, wire, configure, and program the planned
maximum configuration of the ET 200S. The electronic modules you require for
this are initially replaced with inexpensive RESERVE modules which are then later
simply exchanged for the required electronic modules.
This means that the ET 200S can be completely prewired (master wiring) because
the RESERVE module is not connected to the terminals of the terminal module or
therefore the process.
The RESERVE modules for future expansion at the right-hand end of the station
are optional. In this case, preparatory installation and wiring are possible but not a
prerequisite.
Note
You can find information on the removal and insertion of electronic modules in
Section 5.5.
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ET 200S Distributed I/O System
EWA-4NEB780602402-09