16 Publication 1756-PM004C-EN-P - October 2009
Chapter 1 Communicate with I/O Modules
Compatible Keying
Compatible Keying indicates that the module determines whether to accept or
reject communication. Different module families, communication adapters,
and module types implement the compatibility check differently based on the
family capabilities and on prior knowledge of compatible products.
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 using the earliest, that is, lowest, revision of the
physical module that you believe will be used in the system.
Changing electronic keying selections online may cause the I/O
Communication connection to the module to be disrupted and
may result in a loss of data.
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