Rockwell Automation 1785-Lxxx Enhanced and Ethernet PLC-5 Programmable Controllers - Manual (Page 244)

Publication 1785-UM012D-EN-P - July 2005
15-6 Preparing Fault Routines
Avoiding Multiple Watchdog Faults
If you encounter a memory loss fault or watchdog major fault, it may be
because multiple watchdog faults occurred while the controller was busy
servicing a ladder-related major fault. The memory loss fault occurs when the
fault queue, which stores a maximum of six faults, becomes full and cannot
store the next fault.
Before calling a service representative when you encounter either a memory
loss fault or multiple watchdog faults, check:
If you continue to encounter the memory loss fault, call your local Rockwell
Automation representative.
Programming a Fault
Routine To prepare your fault-routine program, first examine the major fault
information recorded by the PLC-5 controller and then decide whether to do
the following before the PLC-5 controller automatically goes to fault mode:
• set an alarm
• clear the fault
• execute the appropriate fault routine through ladder logic
• execute the appropriate ladder logic to recover from a fault
If You Encounter Then
watchdog error and
a fault bit Extend the watchdog timer so that the real run-time error is not
masked.
Check your major fault bits. Ignore the watchdog faults and use
any remaining fault bits to help indicate the source of the
controller fault.
memory loss fault 1.Power down then power up the controller.
2.Reload the program.
3.Set the watchdog timer to a value = 10 current setting
4.Run the program again.
IMPORTANT
If the PLC-5 controller detects a fault in the fault routine
(double-fault condition), the PLC-5 controller goes directly
to fault mode without completing the fault routine.