Siemens SIMATIC S7-1500 Automation System System Manual page 102

Commissioning
8.4 Operating modes
Hardware compatibility
Compatible means that the module matches the number of inputs and output and must
match with respect to its electrical and functional properties. A compatible module must be
fully able to replace a configured module; it may be more capable, but not less capable.
In case of the "Startup of the CPU only if compatible" setting the CPU only starts up if the
configured module or a compatible module is inserted. The CPU does not start up if an
incompatible module is inserted.
Example for the "Startup of the CPU only if compatible" setting:
The input module DI 32x24VDC HF with 32 digital inputs is a compatible replacement for the
input module DI 16x24VDC HF with 16 digital inputs, because the pin assignment and all the
electrical and functional properties agree.
Example for the "Startup of the CPU even if there are differences" setting:
Instead of a configured digital input module an analog output module is plugged or no
module is present in this slot. Although the configured inputs cannot be accessed, the CPU
starts up.
Note in this case that the user program cannot function correctly, so take the appropriate
measures!
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S7-1500 Automation System
System Manual, 01/2013, A5E03461182-01