Rockwell Automation 1756-XXXX ControlLogix Digital I/O Modules - Manual (Page 43)

Rockwell Automation Publication 1756-UM058G-EN-P - November 2012 43
Common Module Features Chapter 3
When a module is created, the module developers consider the module’s
development history to implement capabilities that emulate those of the previous
module. However, the developers cannot know future developments. Because of
this, when a system is configured, we recommend that you configure your module
by using the earliest, that is, lowest, revision of the physical module that you
believe will be used in the system. By doing this, you can avoid the case of a
physical module rejecting the keying request because it is an earlier revision than
the one configured in the software.
EXAMPLE In the following scenario, Compatible Keying prevents I/O
communication.
The module configuration is for a 1756-IB16D module with module revision
3.3. The physical module is a 1756-IB16D module with module revision 3.2. In
this case, communication is prevented because the minor revision of the
module is lower than expected and may not be compatible with 3.3.
Module Configuration
Vendor = Allen-Bradley
Product Type = Digital Input Module
Catalog Number = 1756-IB16D
Major Revision = 3
Minor Revision = 3
Physical Module
Vendor = Allen-Bradley
Product Type = Digital Input Module
Catalog Number = 1756-IB16D
Major Revision = 3
Minor Revision = 2
Communication is prevented