Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules - Manual (Page 40)

40 Publication 1756-UM009C-EN-P - December 2010
Chapter 3 ControlLogix Analog I/O Module Features
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.
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 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