Rockwell Automation 1757-FFLDC4 FOUNDATION Fieldbus System User Manual - Manual (Page 96)

96 Rockwell Automation Publication 1757-UM012A-EN-P - July 2011
Chapter 5 Create an RSLogix 5000 Software Project
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.
EXAMPLE In the following scenario, Exact Match keying prevents I/O communication.
The module configuration is for a 1756-IB16D module with module revision 3.1. 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
does not match precisely.
Module Configuration
Vendor = Allen-Bradley
Product Type = Digital Input
Module
Catalog Number = 1756-IB16D
Major Revision = 3
Minor Revision = 1
Communication is prevented.
Physical Module
Vendor = Allen-Bradley
Product Type = Digital Input
Module
Catalog Number = 1756-IB16D
Major Revision = 3
Minor Revision = 2
IMPORTANT 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.