Bradley Smoker PLC-5 Instructions with Unique Prescan Operations, Awt Awa Acb Abl Ahl Btr, Fnd

F-10Troubleshooting

Unexpected Operation when Entering Run Mode

If unexpected operation occurs whenever your controller enters run mode, be sure to examine the prescan operation of the instructions in this section. These instructions execute differently during prescan than they do during a normal scan.

The prescan function is an intermediate scan between the transition from program to run modes, during which all rungs are scanned as false. The prescan examines all ladder program files and instructions and initializes the data table based on the results of the program.

For example, a subroutine that is called infrequently may contain a bad indirect address and generate a major fault. However, many normal program scans may occur before the major fault is actually generated. Prescan provides the opportunity for the controller to examine the program for errors such as this before transitioning to Run mode.

Instructions with Unique Prescan Operations

Use the table below to track prescan operations that deviate from normal instruction operation.

This	Executes These Actions During Prescan:
Instruction:
ARD	If the EN bit is set and the DN and ER bits are cleared, then the control
	word is cleared. If either the DN or ER bit is set, then the EN bit is
ARL
	cleared and the DN bit is set.
AWT
AWA
ACB
ABL
AHL
BTR	All non-user configuration bits 15, 14, 13, 12, 10, and 9 are cleared (for
	both INT and BT file types).
BTW
CTU	The CU/CD bit is set to prevent a false count when the first run-mode
	scan begins.
CTD
EOT	This instruction is skipped so all ladder instructions can be prescanned.
FFL	The EL bit is set to prevent a false load when the first run-mode scan
	begins.
LFL
FFU	The EU bit is set to prevent a false unload when the first run-mode scan
	begins.
LFU
FND	This instruction is skipped so all ladder instructions can be prescanned.

Publication 1785-UM012D-EN-P - July 2005