482 Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Chapter 11 Program Control Instructions (JMP, LBL, JSR, RET, SBR, JXR, TND, MCR, UID, UIE, AFI, NOP, EOT, SFP, SFR, EVENT)
The controller does not clear the bits of the Status attribute once they are set.
· To use a bit for new status information, you must manually clear the bit.
· Use a Set System Value (SSV) instruction to set the attribute to a different
value.
Arithmetic Status Flags: Not affected
Fault Conditions: None
Execution:
Example 1: A controller uses multiple programs but a common shut down procedure. Each
program uses a program-scoped tag named Shut_Down_Line that turns on if the
program detects a condition that requires a shut down. The logic in each program
executes as follows:
If Shut_Down_Line = on (conditions require a shut down) then
Execute the Shut_Down task one time
Relay Ladder
Program A
Program B
Condition Relay Ladder Action Structured Text Action
Prescan The rung-condition-out is set to false. No action taken.
Rung-condition-in is false The rung-condition-out is set to false. N/A
Rung-condition-in is true The instruction executes. N/A
The rung-condition-out is set to true.
EnableIn is set N/A EnableIn is always set.
The instruction executes.
Instruction execution The instruction triggers one execution of the specified event task
Postscan The rung-condition-out is set to false. No action taken.
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