Rockwell Automation Publication 1756-PM014N-EN-P - March 2022 9
Chapter 1
Major Faults
This chapter explains major fault codes and how to work with them in the
Logix Designer application.
If a fault condition occurs that prevents an instruction from running, the
instruction aborts and the controller reports a major fault. A major fault halts
logic execution and the controller switches to faulted mode (the OK LED
flashes red).
Depending on the application, you may not want all major faults to shut down
the system. If you do not want all major faults to shut down the system, create
a fault routine to clear the fault and let the application continue to run.
The process of resuming execution after the fault clears is known as fault
recovery.
Do not use fault routines to continually clear all faults on the controller. Program the fault
routine to be selective in the types and number of faults cleared. It is also a good idea to log
the fault occurrence to analyze it later.
When an instruction generates an error due to a fault (for example, a COP with an indirect
addressing programming error), the fault routine skips the instruction and does not run. This
occurs with all instructions.
In a system that uses recipe numbers as indirect addresses, an incorrectly typed number could
produce a major fault.
To keep the entire system from shutting down in the event of this fault, program a fault routine to
clear type 4, code 20, major faults.
See also
Create a routine for the controller fault handler on page 16
Clear a major fault during prescan on page 22
These examples show fault routines with logic that take specific action after a
major fault. If the fault clears, the faulted instruction does not run and
execution resumes with the next instruction.
Recover from a major fault
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