Programming the Structure of the Sequencer
S7-GRAPH for S7 300/400 Programming Sequential Control Systems
6-2 C79000-G7076-C526-01
6.1 Sequencer - Principle
A sequencer consists of a series of steps and transitions that are activated in a
fixed order depending on the step enabling conditions.
How a Sequencer is Executed
A sequencer is always executed starting with
• an initial step or
• several initial steps located at any position in the sequencer.
As long as the actions of a step are being
executed, this step is active. If several steps are being executed
at the same time, they are all active steps.
↓
An active step is exited when
• all disturbances have been cleared or confirmed
• and the transition following the step is satisfied.
↓
The next step following the satisfied transition becomes active.
↓
At the end of a sequencer, there is
• a jump to any step in this sequencer or in another sequencer of the FB.
This allows cyclic operation of the sequencer
• a branch stop. The sequence of steps stops when the branch stop is reached.
Step
The control task is divided into single steps. Actions are formulated in the steps
that are executed by the controller in a certain status (for example for controlling
the outputs or activating/deactivating steps).
Active Step
An active step is a step whose actions are currently being executed.
A step is activated, as follows:
• When the conditions of the previous transition are satisfied or
• When the step is defined as an initial step and the sequencer has been
initialized or
• When it is called by an event-dependent action.
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