Allen-Bradley 1756-L61 ControlLogix 5561 Programming Manual page 19

Communicate with I/O Modules Chapter 1
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.
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.
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.
ATTENTION: In the following scenario, Disable Keying prevents I/O
EXAMPLE
communication:
ATTENTION: The module configuration is for a 1756-IA16 digital input module.
The physical module is a 1756-IF16 analog input module. In this case,
communication is prevented because the analog module rejects the
data formats that the digital module configuration requests.
Module Configuration
Vendor = Allen-Bradley
Product Type = Digital Input
Module
Catalog Number = 1756-IA16
Major Revision = 3
Minor Revision = 1
Physical Module
Vendor = Allen-Bradley
Product Type = Analog Input Module
Catalog Number = 1756-IF16
Major Revision = 3
Minor Revision = 2
Rockwell Automation Publication 1756-PM004D-EN-P - September 2012
Communication is prevented
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