Publication 1756-PM004C-EN-P - October 2009 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.
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.
Be extremely cautious when using Disabled Keying; if used
incorrectly, this option can lead to personal injury or death,
property damage, or economic loss.
In the following scenario, Disable Keying prevents I/O
communication:
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
Communication is prevented
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