Rockwell Automation 1756-HSC ControlLogix High Speed Counter Module - Manual (Page 76)

Rockwell Automation Publication 1756-UM007C-EN-P - November 2011
76 Configure the 1756-HSC Module
Compatible Keying is the default setting. Compatible Keying allows the
physical module to accept the key of the module configured in the software,
provided that the configured module is one the physical module is capable of
emulating. The exact level of emulation required is product and revision
specific.
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.