Rockwell Automation 1769-ASCII Compact I/O ASCII Module - Manual (Page 108)

108 Rockwell Automation Publication 1769-UM012B-EN-P - January 2014
Appendix E Using Electronic Keying
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.
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.