Rockwell Automation 1785 PLC-5 User Manual download pdf (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.

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Rockwell Automation 1785 PLC-5 User Manual Page 244