Trigger Event Task (EVENT)

The EVENT instruction triggers one execution of an event task.

Available Languages

Ladder Diagram

Function Block

This instruction is not available in function block.

Structured Text

EVENT(task_name);

Operands

Ladder Diagram

Structured Text

See Structured Text Syntax for more information on the syntax of expressions within structured text.

Description

Use the EVENT instruction to programmatically execute an event task.

Each time the instruction executes, it trigger the specified event task.

Make sure that you give the event task enough time to complete its execution before you trigger it again. If not, an overlap occurs.

If you execute an EVENT instruction while the event task is already executing, the controller increments the overlap counter, but it does not trigger the event task.

EVENT instruction can be used to trigger Event Task with all the trigger types.

Programmatically Determine if an EVENT Instruction Triggered a Task

To determine if an EVENT instruction triggered an event task, use a Get System Value (GSV) instruction to monitor the Status attribute of the task.

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.

Affects Math Status Flags

No

Fault Conditions

None specific to this instruction. See Common Attributes for operand-related faults.

Execution

Ladder Diagram

Structured Text

Examples

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

Ladder Diagram

Program A

Program B

Structured Text

Program A

IF Shut_Down_Line AND NOT Shut_Down_Line_One_Shot THEN

EVENT (Shut_Down);

END_IF;

Shut_Down_Line_One_Shot:=Shut_Down_Line;

Program B

IF Shut_Down_Line AND NOT Shut_Down_Line_One_Shot THEN

EVENT (Shut_Down);

END_IF;

Shut_Down_Line_One_Shot:=Shut_Down_Line;

Example 2

The following example uses an EVENT instruction to initialize an event task. Another type of event normally triggers the event task.

Continuous Task

IF Initialize_Task_1 = 1 THEN

The ONS instruction limits the execution of the EVENT instruction to 1 scan.

The EVENT instruction triggers an execution of Task_1 (event task).

Task_1 (event task)

The GSV instruction sets Task_Status (DINT tag) = Status attribute for the event task. In the Instance Name attribute, THIS means the TASK object for the task that the instruction is in (e.g., Task_1).

If Task_Status.0=1 then an EVENT instruction triggered the event task (i.e., when the continuous task executes its EVENT instruction to initialize the event task).

The RES instruction resets a counter the event task uses.

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.

If Task_Status.0 = 1 then clear that bit.

The OTU instruction sets Task_Status.0 = 0.

The SSV instruction sets the Status attribute of THIS task (Task_1) = Task_Status. This includes the cleared bit.