44 Rockwell Automation Publication 1756-UM058G-EN-P - November 2012
Chapter 3 Common Module Features
Disabled Keying
Disabled Keying indicates the keying attributes are not considered when
attempting to communicate with a module. Other attributes, such as data size
and format, are considered and must be acceptable before I/O communication is
established. With Disabled Keying, I/O communication may occur with a
module other than the type specified in the I/O Configuration tree with
unpredictable results. We generally do not recommend using Disabled Keying.
If you use Disabled Keying, you must take full responsibility for understanding
whether the module being used can fulfill the functional requirements of the
application.
In the following scenario, Compatible Keying allows I/O communication.
The module configuration is for a 1756-IB16D module with module revision
2.1. The physical module is a 1756-IB16D module with module revision 3.2. In
this case, communication is allowed because the major revision of the physical
module is higher than expected and the module determines that it is
compatible with the prior major revision.
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.
ATTENTION: Be extremely cautious when using Disabled Keying; if used
incorrectly, this option can lead to personal injury or death, property damage,
or economic loss.
Module Configuration
Vendor = Allen-Bradley
Product Type = Digital Input Module
Catalog Number = 1756-IB16D
Major Revision = 2
Minor Revision = 1
Physical Module
Vendor = Allen-Bradley
Product Type = Digital Input Module
Catalog Number = 1756-IB16D
Major Revision = 3
Minor Revision = 2
Communication is allowed
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