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
Not Available
Function Block
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Sequential Function Chart
Action:
action_avail
Boolean Action:
Boolean action instruction
Structured Text
Not Available
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:
  • S Stored
  • SL Stored and Time Limited
  • DS Delayed and Stored
  • SD Stored and Time Delayed
action_rtarrow
R
Reset
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