State

(TcoState : ITcoState)

API

The state controller TcoState manages states of the system.

TcoState holds the control variable and manages the change via TcoState.ChangeState(newState).

The override of the TcoState.OnStateChange(lastState, newState) method allows to perform operation on transition between the states.

IF(State = 10) THEN
    IF(a.DoSomething().Done) THEN
        ChangeState(20).Restore(VerticalCylinder).Restore(HorizontalCylinder);  // Change state and restore objects
    END_IF;    
END_IF;    

IF(s.State = 20) THEN
    IF(VerticalCylinder.DoSomething().Done) THEN
        ChangeState(10);    
    END_IF;    
END_IF;    

//--------------------------------------------------
// Override of OnStateChange method
//--------------------------------------------------
METHOD PROTECTED OnStateChange
VAR_INPUT
	PreviousState	: INT;
	NewState 		: INT;
END_VAR

// On transition to state 10
IF(NewState = 10) THEN
    logger.Log('Transitioning to state no 10');
    VerticalCylinder.Restore();
END_IF;

Restoring state of objects

The restorable objects alleviate the burden of finding the right place and time for restoring objects in the PLC program.

Any object that implements correctly ITcoRestorable is eligible for implicit auto-restore. ITcoRestorable.Restore() method must implement the logic that brings the object to the initial state Ready and thus make it ready for the new execution.

We already mentioned restoring mechanisms in the section about ITcoTask. The example above demonstrates two ways of performing explicit the auto restore:

  1. In the state 10 call
s.ChangeState(20).Restore(VerticalCylinder).Restore(HorizontalCylinder)

restores the state of the object VerticalCylinder and HorizontalCylinder;

  1. In the override OnStateChange, we restore only object VerticalCylinder.

Implicit restoring mechanism restores object without explicit coding. There are two ways the object can be restored:

  1. The objects that are directly declared in the body of the object of ITcoState will be restored when

    1. The ITcoState changes state,
    2. ITcoState is configured auto-restorable,
    3. IRestorable object is a direct member of the ITcoState.

In this case, the state of the child objects (ITcoObject declared directly in the state block) is restored when the state of the parent ITcoState changes.

//---------------------------------------------------------
FUNCTION_BLOCK MyContext EXTENDS TcoCore.TcoContext
VAR
    // AutoRestoreMembers INDICATES THE STATES MEMBERS ARE AUTO-RESTORABLE
    _myState : MyStateController(THIS^, eRestoreMode.AutoRestoreMembers); 
END_VAR   
//---------------------------------------------------------
FUNCTION_BLOCK MyStateController : EXTENDS TcoCore.TcoState
VAR
    VerticalCylinder : MyComponentThasDoesSomething(THIS^);
END_VAR;    

IF(State = 10) THEN
    IF(VerticalCylinder.DoSomething().Done) THEN
        ChangeState(20); 
    END_IF;    
END_IF;    

IF(s.State = 20) THEN
    IF(VerticalCylinder.DoSomething().Done) THEN
        ChangeState(10);    
    END_IF;    
END_IF;
  1. The classes that implement the auto-restorable mechanism (TcoTask) will restore its state upon the call of the method executing an action, provided that there were at least two consecutive cycles of the context where that executing method was not called.