Start
This function realizes the initial step of the sequence control. It is a special form of the Step function block.
At the beginning of runtime, the Start block automatically gets a token. A Start block is used to initiate a flow control and normally cannot get a token later on. Only by a preset, the Start block can get a token at run time. With the Preset function block, the flow control is set to a predefined state and so a Start block can get a token again.
This function block contains the outputs SO and SM. The output SM is a BIT data type. It shows if this block has a token or not. SO has to be connected with a transition. Over this transition the token will be transferred.
For general information about sequence function and its realization see introduction.
Signals
| Name | I/O | Type(s) | Function |
|---|---|---|---|
| SO | O | TOTRANS | Sequence output |
| SM | O | BIT | State (token) |
Visualization
If this initial step is currently active, the symbol will be depicted in green. If the function block is connected in a way, which is potentially harmful for the control flow (e.g. aggregation of tokens), it will be depicted in yellow.
Comment
All flow controls within a structure block are part of the same flow control net. A macro block can be a part of a flow control. For connecting a macro with a flow control block, use the connectors of the type TOTRANS or TOSTEP.