Equipment Sequence command (SCMD)

This instruction applies to the
Logix Designer
 5580 P-controllers. The
Logix Designer
 5580 P-controllers also support controller redundancy.
TIP:
When using this instruction with
ControlLogix
 redundancy system, outputs controlled by this instruction may not be bumpless during redundancy switchover, if the instruction and sequence program are not scheduled in the highest priority task.
WARNING:
When using redundancy with an
Equipment Sequence
, sequence execution may not be as expected after switchover if the phase and sequence are not scheduled on the same task.
Use the
Equipment Sequence
 command (SCMD) instruction to change the state of an
Equipment Sequence
. The SCMD instruction can send these commands to an
Equipment Sequence
: START, RESTART, HOLD, STOP, ABORT, RESET, PAUSE, RESUME, and AUTOPAUSE. The calling program must either be attached as owner to the
Equipment Sequence
 or there is no owner of the
Equipment Sequence
 before the SCMD instruction can run. Use the SATT instruction to attach to an
Equipment Sequence
. In addition, the
Equipment Sequence
 must be in the correct state (see chart below) for the command to execute successfully.
Like the SCMD instruction, the
Equipment Sequence
 Override instruction (SOVR) also changes the state of an
Equipment Sequence
, but it changes the state regardless of ownership. If the SCMD instruction must execute regardless of ownership, use an SOVR instruction instead of an SCMD instruction.
IMPORTANT:
The SOVR instruction is intended for emergencies only. Control Engineers should use caution when deciding to use it.
When a tag is assigned to store the result of an SCMD instruction, the instruction returns one of five result codes when it runs. Result code 0 indicates that the SCMD instruction ran successfully. The other four codes indicate that the instruction did not run successfully and provide additional information about the reason for the instruction failure.
This is a transitional instruction. Follow these steps when using it:
  • In ladder logic, insert an instruction to toggle the rung-condition-in from false to true each time the instruction should execute.
  • In a Structured Text routine, insert a condition for the instruction to cause it to execute only on a transition.
Valid command states for the SCMD instruction
The SCMD instruction command transitions an
Equipment Sequence
 to another state. SCMD instruction commands may only be processed in certain states, with the exceptions of PAUSE, RESUME, and AUTOPAUSE, which are valid in all states. The 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.
Available Languages
Ladder Diagram
SCMD_LD_avail_v34
Function Block
This instruction is not available in function block.
Structured Text
SCMD(Sequence Name, Sequence Command, Result)
Operands
Ladder Diagram
Operand
Data Type
Format
Description
Sequence Name
SEQUENCE
Name of the
Equipment Sequence
Equipment Sequence
 to perform the command.
Command
Command Enum
Enumeration of the command
Command to send to the
Equipment Sequence
. Send one of these commands: START, RESTART, HOLD, STOP, ABORT, RESET, PAUSE, RESUME, or AUTOPAUSE.
Result
DINT
Tag
For an instruction to return a success or failure code, enter a DINT tag where the result code is stored. Otherwise, enter 0.
Structured Text
The operands are the same as for the Ladder Diagram.
Guidelines for using the SCMD Instruction
Guideline
Details
Limit execution of the SCMD instruction to a single scan.
Limit the execution of the SCMD instruction to a single scan. Each command applies to only a specific state or states. Once the
Equipment Sequence
 changes state, the command is no longer valid. To limit execution, use methods such as:
Run the SCMD instruction within a P1 Pulse (Rising Edge) or P0 Pulse (Falling Edge) action.
Place a one-shot instruction before the SCMD instruction.
Run the SCMD instruction and then advance to the next step.
The
Equipment Sequence
 must be either owned by the program to command it or have no owners for the program to command it.
The ownership instructions are Attach (SATT) and Detach (SDET).
SCMD Result Codes
Code (Desc)
Description
0
The command was successful.
24578
The command is not valid for the current state of the Sequence.
24579
The caller is attached to this Sequence, but it is not the current Owner of it. A higher priority application is currently the Owner of this sequence.
24580
The caller is not attached to the Sequence.
24594
The
Equipment Sequence
 is unscheduled, inhibited, or in a task that is inhibited.
24604
An equal or higher priority command is being processed.
24631
Too many sequence parameter or step tags are defined per step, so events cannot be handled and the START command failed.
Arithmetic Math Status Flags
No
Major/Minor Faults
None specific to this instruction. See Index Through Arrays for operand related faults.
Execution
At instruction execution, the SCMD instruction commands the specified
Equipment Sequence
.
Ladder Diagram
Condition
Action Taken
Prescan
No action taken
Rung-condition-in is false
No action taken
Rung-condition-in is true
The instruction executes.
Postscan
No action taken
Structured Text
Condition
Action Taken
Prescan
No action taken
Rung-condition-in is false
No action taken
Rung-condition-in is true
The instruction executes.
Postscan
No action taken
Example
Ladder Diagram
SCMD_LadderLogix_Example_v34
Structured Text
if (CommandControl) then
SCMD(Make_Product_101, Start, Result);
end_if
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