Bradley Smoker PLC-5 user manual Understanding, Faults, General, It Sets

15-2Preparing Fault Routines

•returns to the current ladder program file if the controller can recover from the fault

•enters fault mode if the controller cannot recover from the fault

For example, this rung includes an instruction that causes a major fault:

A

[ [

BC

Causes a major fault

In this example, the processor runs the fault routine after detecting the fault. If the fault routine resets the faulted bits, the processor returns to the next instruction in the program file that follows the one that faulted and continues executing the remainder of the rung.

If you do not program a fault routine for fault B, the processor immediately faults.

Understanding

Controller-Detected Major

Faults

In general:

If the Controller Detects a	It Sets
major fault	a major fault bit and resets I/O
memory loss fault	outputs in 1771-ASB remote I/O racks and/or 1771-ALX
	extended-local I/O racks are set according to their last
	state switch setting
	The outputs remain in their last state or they are
	de-energized, based on how you set the last state switch
	in the I/O chassis.

IMPORTANT

In the PLC-5 controller-resident chassis, outputs are reset regardless of the last state switch setting when one of the following occurs:

•controller detects a major fault

•you set a status file bit to reset a local rack

•you select program or test mode

Publication 1785-UM012D-EN-P - July 2005