Status File Data Saved; Creating A User Fault Subroutine - Allen-Bradley SLC 500 Series Reference Manual

Status File Data Saved

Data in the following words is saved on entry to the user fault subroutine and
re-written upon exiting the subroutine.
• S:0 Arithmetic flags
• S:13 and S:14 Math register
• S:24 Index register

Creating a User Fault Subroutine

To use the user fault subroutine:
1. Create a subroutine file: valid range is 3-255.
2. Enter the file number in word S:29 of the status file.
Project Tree - Controller Folder - Processor Status File - Errors Tab
The occurrence of recoverable or non-recoverable user faults causes the
processor to read S:29 and execute the subroutine number contained in 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 processor then continues in the REM Run
mode.
The routine does not execute for non-user faults.
Words S:20 and S:21 can be examined in your fault routine to pinpoint the file
and rung number where the fault occurred. If the fault occurred outside of the
ladder scan, this value will contain the rung number where the TND, END, or
REF instruction is located. Use words S:20 and S:21 with your power-up
protection fault routine to determine the exact point that the previous power
down occurred.
Understanding Interrupt Routines
Publication 1747-RM001G-EN-P - November 2008
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