Rockwell Automation 1756-CFM ControlLogix Configurable Flowmeter Module - Manual (Page 30)

30 Rockwell Automation Publication 1756-UM010B-EN-P - December 2011
30 Configurable Flowmeter Module Features and Operational Modes
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.
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 this 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
Communication is prevented.