Allen-Bradley LOGIX 5000 Reference Manual page 475

Equipment Sequence
Condition
Prescan
Rung-condition-in is false
Rung-condition-in is true
Scan of structured text
Instruction execution
Postscan
Condition
Prescan
Rung-condition-in is false
Rung-condition-in is true
Scan of structured text
Instruction execution
Valid command states for the SCMD instruction
Use the SCMD instruction transitions to command an Equipment Sequence to
another state. The SCMD instruction commands may only be processed in certain
states. The following table lists the states in which commands are valid.
Command Valid in these states
START Valid in the IDLE state.
RESTART Valid in the HELD state.
HOLD Valid in the RUNNING and RESTARTING states.
STOP Valid in the RUNNING, HOLDING, RESTARTING, and HELD states.
ABORT Valid in the RUNNING, HOLDING, RESTARTING, STOPPING, and HELD states.
RESET Valid in the ABORTED, STOPPED, and COMPLETE states.
Arithmetic status flags and fault conditions
Arithmetic status flags are not affected by the SCMD instruction. The SCMD
instruction cannot trigger a fault, so there are no fault conditions for this
instruction.
Execution
Ladder Diagram
Structured Text
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018
Action Taken
The rung-condition-out is set to false.
The rung-condition-out is set to false.
The instruction executes.
The rung-condition-out is set to true.
No action taken
The instruction tries to take ownership of the specified Equipment
Sequence.
The rung-condition-out is set to false.
Action Taken
No action taken.
No action taken.
No action taken.
In structured text, instructions execute each time they are scanned. To
limit the scan of an instruction, use a qualifier of an SFC action or a
structured text construct.
The instruction tries to take ownership of the specified Equipment
Sequence.
Chapter 8
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