Step
The Step represents a major function of your process. It contains the events that occur during a particular time, phase, or station.
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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.
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).
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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.
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flag if a step is executing too long | LimitHigh | DINT | Enter the time in the LimitHigh member (milliseconds).
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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.
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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.
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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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