Action and Boolean Action
In a sequential function chart (SFC), an action represents a functional division of a step. Several actions make up a step. Each action performs a specific function, such as controlling a motor, opening a valve, or placing a group of devices in a specific mode.
While an Action may contain Structure Text logic, a Boolean Action contains no logic for the action. It simply sets a bit in its tag (SFC_ACTION structure). To do the action, other logic must monitor the bit and execute when the bit is on. With Boolean Actions, you have to manually reset the assignments and instructions that are associated with the action. Because there is no link between the action and the logic that performs the action, the automatic reset option does not affect Boolean Actions.
Available Languages
Ladder Diagram |
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Function Block |
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Sequential Function Chart |
Action:  Boolean Action:  |
Structured Text |
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Operands
Sequential Function Chart
Operand | Type | Format | Description |
Action | SFC_ACTION | tag
ST logic | A functional division of a step. |
Description
There are two types of actions.
If you want to | Then |
have your logic monitor the status of the action and execute when the action is active | define the action as a Boolean action. |
execute structured text directly in the action. | do not define the action as a Boolean action. |
use the action to call another routine. |
Each action includes a qualifier. When a step is active (executing) the qualifier determines when the action starts and stops. Each action uses a backing tag that provides information about the action. The following information is available via either the
Action Properties
dialog box or the Tags
window.If you want to | Then check or set this number | Data Type | Details | |
|---|---|---|---|---|
determine when the action is active | Q | BOOL | The status of the Q bit depends on whether the action is a Boolean action or not a Boolean action. | |
If the action is | Then the Q bit is | |||
Boolean | on (1) when the action is active. | |||
not Boolean | off (0) at the last scan of the action. | |||
Typically, to use a bit to determine when an action is active, use the Q bit. | ||||
A | BOOL | The A bit is on when the action is active. | ||
determine how long an action has been active (milliseconds) | T | DINT | When a action becomes active, the Timer (T) value resets and then starts to count up in milliseconds. The timer continues to count up until the action goes inactive, regardless of the Preset (PRE) value. | |
use one of these time-based qualifiers: L, SL, D, DS, SD | PRE | DINT | Enter the time limit or delay in the Preset (PRE) member. The action starts or stops when the Timer (T) reaches the Preset value. | |
determine how many times an action has become active | Count | DINT | This is not a count of scans of the action. The count increments each time the action becomes active. It increments again only after the action goes inactive and then active again. | |
use one tag for the various status bits of this action | Status | DINT | For this member | Use this bit |
Q | 30 | |||
A | 31 |
Qualifier
In the action of a sequential function chart (SFC), a qualifier defines when the action starts and stops.
If you want the action to | And | Then assign this qualifier | Which Means |
|---|---|---|---|
start when the step is activated | stop when the step is deactivated | N | Non-Stored |
execute only once | P1 | Pulse (Rising Edge) | |
stop before the step is deactivated | L | Time Limited | |
stay active until a Reset action turns off this action | S | Stored | |
continue for a specific time, even if the step is deactivated | SL | Stored and Time Limited | |
start a specific time after the step is activated (step must still be active) | stay active until a Reset action turns off this action | D | Time Delayed |
stay active until a Reset action turns off this action | DS | Delayed and Stored | |
start a specific time after the step is activated, even if the step is deactivated before this time | stay active until a Reset action turns off this action | SD | Stored and Time Delayed |
execute once when the step is activated | execute once when the step is deactivated | P | Pulse |
start when the step is deactivated | execute only once | PO | Pulse (Falling Edge) |
turn off (reset) one of these actions of another step:
|  | R | Reset |
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