Step

The Step represents a major function of your process. It contains the events that occur during a particular time, phase, or station.
stepaction
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Operands
Sequential Function Chart
Operand
Type
Format
Description
Step
SFC_STEP
tag
a major function of your process containing events done during a particular time, phase, or station.
Description
The simplest way to connect steps is in sequence.
stephowto
Each step uses a backing tag that provides information about the step. The following information is available via either the Step Properties dialog box or the Tags window.
If you want to
Then Check or set this member
Data type
Details
determine how long a step has been active (milliseconds)
T
DINT
When a step becomes active, the Timer (T) value resets and then starts to count up in milliseconds. The timer continues to count up until the step goes inactive, regardless of the Preset (PRE) value.
flag when the step has been active for a specific length of time (milliseconds)
PRE
DINT
Enter the time in the Preset (PRE) member. When the Timer (T) reaches the Preset value, the Done (DN) bit turns on and stays on until the step becomes active again.
DN
BOOL
When the Timer (T) reaches the Preset (PRE) value, the Done (DN) bit turns on and stays on until the step becomes active again.
flag if a step did not execute long enough
LimitLow
DINT
Enter the time in the LimitLow member (milliseconds).
  • If the step goes inactive before the Timer (T) reaches the LimitLow value, the AlarmLow bit turns on.
  • The bit stays on until you reset it.
  • To use this alarm function, turn on (check) the AlarmEnable (AlarmEn) bit.
AlarmEn
BOOL
To use the alarm bits, turn on (check) the AlarmEnable (AlarmEn) bit.
AlarmLow
BOOL
If the step goes inactive before the Timer (T) reaches the LimitLow value, the AlarmLow bit turns on.
  • The bit stays on until you reset it.
  • To use this alarm function, turn on (check) the AlarmEnable (AlarmEn) bit.
flag if a step is executing too long
LimitHigh
DINT
Enter the time in the LimitHigh member (milliseconds).
  • If the Timer (T) reaches the LimitHigh value, the AlarmHigh bit turns on.
  • The bit stays on until you reset it.
  • To use this alarm function, turn on (check) the AlarmEnable (AlarmEn) bit.
AlarmEn
BOOL
To use the alarm bits, turn on (check) the AlarmEnable (AlarmEn) bit.
AlarmHigh
BOOL
If the Timer (T) reaches the LimitHigh value, the AlarmHigh bit turns on.
  • The bit stays on until you reset it.
  • To use this alarm function, turn on (check) the AlarmEnable (AlarmEn) bit.
do something while the step becomes active
X
BOOL
Use this bit for a step that does not have any actions.
Typically, we recommend that you use an action with a N Non-Stored qualifier to accomplish this.
do something one time when the step becomes active
FS
BOOL
Use this bit for a step that does not have any actions. Or use this bit when all the logic for the step is called by or embedded in a single action.
Typically, we recommend that you use an action with a P1 Pulse (Rising Edge) qualifier to accomplish this.
do something while the step is active, except on the first and last scan
SA
BOOL
Use this bit for a step that does not have any actions. Or use this bit when all the logic for the step is called by or embedded in a single action.
do something one time on the last scan of the step
LS
BOOL
Use this bit for a step that does not have any actions. Or use this bit when all the logic for the step is called by or embedded in a single action.
Use this bit only if you do the following: On the Controller Properties dialog box, SFC Execution tab, set the Last Scan of Active Step to Programmatic reset.
Typically, we recommend that you use an action with a P0 Pulse (Falling Edge) qualifier to accomplish this.
determine to which step an SFC Reset (SFR) instruction has set the SFC
Reset
BOOL
The Reset bit marks the step that will execute when an SFC Pause (SFP) instruction resumes the execution of the SFC.
  • When an SFC Reset (SFR) instruction executes, it pauses the SFC chart and sets the Reset bit of a step in the SFC.
  • To resume the execution of the SFC, execute an SFC Pause (SFP) instruction. This instruction starts the SFC at the step with the Reset bit on and then clears the Reset bit.
determine the maximum time that a step has been active during any of its executions
TMax
DINT
Use this for diagnostic purposes.
determine if the Timer (T) value has exceeded it upper limit
OV
BOOL
Use this for diagnostic purposes.
determine how many times a step has become active
Count
DINT
This is
not
a count of scans of the step. The count increments each time the step becomes active. It increments again only after the step goes inactive and then active again.
use one tag for the various status bits of this step
Status
DINT
For This Member:
Use This Bit:
Reset
22
AlarmHigh
23
AlarmLow
24
AlarmEn
25
OV
26
DN
27
LS
28
SA
29
FS
30
X
31
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