Allen-Bradley MicroLogix 1200 Reference Manual page 226

18-6 Using Interrupts
Publication 1762-RM001C-EN-P
User Fault Routine
The user fault routine gives you the option of preventing a controller
shutdown when a specific user fault occurs. The fault routine is executed
when any recoverable or non-recoverable user fault occurs. The fault
routine is not executed for non-user faults.
Faults are classified as recoverable, non-recoverable, and non-user faults.
A complete list of faults is shown in Fault Messages and Error Codes on
page D-1. The basic types of faults are described below:
Recoverable
Recoverable Faults are caused by
the user and may be recovered
from by executing logic in the
user fault routine. The user can
attempt to clear the Major Error
Halted bit, S:1/13.
Note: You may initiate a MSG
instruction from the controller to
another device to identify the
fault condition of the controller.
Status File Data Saved
The Arithmetic Flags (Status File word S:0) are saved on entry to the user
fault subroutine and re-written upon exiting the subroutine.
Creating a User Fault Subroutine
To use the user fault subroutine:
1. Create a subroutine file. Program Files 3 to 255 can be used.
2. Enter the file number in word S:29 of the status file.
Controller Operation
The occurrence of recoverable or non-recoverable faults causes the
controller to read S:29 and execute the subroutine number identified by
S:29. If the fault is recoverable, the routine can be used to correct the
problem and clear the fault bit S:1/13. The controller then continues in its
current executing mode. The routine does not execute for non-user faults.
Non-Recoverable
Non-Recoverable Faults are
caused by the user, and
cannot be recovered from. The
user fault routine executes
when this type of fault occurs.
However, the fault cannot be
cleared.
Note: You may initiate a MSG
instruction to another device
to identify the fault condition
of the controller.
Non-User Fault
Non-User Faults are caused by
various conditions that cease
ladder program execution. The
user fault routine does not
execute when this type of
fault occurs.