Rockwell Automation 1756-XXXX ControlLogix Digital I/O Modules User Manual
Page 81
Rockwell Automation Publication 1756-UM058G-EN-P - November 2012
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Diagnostic Module Features
Chapter 4
Fault and Status Reporting
between Output Modules
and Controllers
ControlLogix diagnostic digital output modules multicast fault and status data to
any owner-controller or listening controller. Like input modules, output modules
maintain a module-fault word, the highest level of fault reporting. However,
some output modules use additional words to indicate fault conditions.
The table lists the fault words and the associated tags that can be examined in
program logic to indicate when a fault has occurred for a diagnostic output
module.
All words are 32-bit, although only the number of bits appropriate for each
module’s density are used. For example, the 1756-OB8 module has a module-
fault word of 32 bits. But, because the module is an 8-point module, only the first
8 bits (0…7) are used in the module-fault word.
Fault bits in the fuse blown word, field-power loss word, no load word and output
verify word are logically entered into the module-fault word. Depending on the
module type, a bit set in the module-fault word can mean multiple things, as
indicated in the table.
Table 14 - Fault Words on Diagnostic Output Modules
Word
Tag Name
Description
Module-fault
Fault
Provides fault summary reporting. Available on all digital output
modules.
Fuse Blown
FuseBlown
Indicates a blown fuse for a point on the module. For more information,
see For more information, see
.
No Load
NoLoad
Indicates a loss of a load from a point on the module. For more
information, see
.
Output Verify
OutputVerify
Indicates when an output is not performing as commanded by the
owner-controller. For more information, see
Table 15 - Bits Set in Module-fault Word
Condition
Bits Set
Communication fault
All 32 bits are set to 1, regardless of the module’s density.
Fuse blown
Only the bit affected is set to 1.
Field-power loss
No load
Output verify