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.
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.
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.