216 Rockwell Automation Publication 1756-UM001M-EN-P - February 2012
Appendix B Using Electronic Keying
With Compatible Keying, you can replace a module of a certain Major Revision
with one of the same catalog number and the same or later, that is higher, Major
Revision. In some cases, the selection makes it possible to use a replacement that is
a different catalog number than the original. For example, you can replace a
1756-CNBR module with a 1756-CN2R module.
The release notes for individual modules indicate the specific compatibility
details.
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
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.
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.
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