The ProgramStateMachineType components consist of a set of References to the Object instances of StateTypes, TransitionTypes, EventTypes and the Methods that collectively define the Program FiniteStateMachine.

Figure 5 – Program References

Figure 5 illustrates the component References that define the associations between two of the ProgramStateMachineType’s states, Ready and Running. The complementary ReferenceTypes have been omitted to simplify the illustration.

The state Objects are instances of the StateType defined in OPC 10000-16. Each state is assigned a unique StateNumber value defined in Table 6. Subtypes of the ProgramStateMachineType can add references from any state to a subordinate or nested StateMachine Object to extend the FiniteStateMachine.

The Halted state is the idle state for a Program. It can be an initial state or a terminal state. As an initial state, the Program Invocation cannot begin execution due to conditions at the Server. As a terminal state, Halted can indicate either a failed or completed Program. A subordinate state or result can be used to distinguish the nature of the termination. The Halted state references four Transition Objects, which identify the allowed state transitions to the Ready state and from the Ready, Running, and Suspended states.

The Ready state indicates that the Program is prepared to begin execution. Programs that are ready to begin upon their creation may transition immediately to the Ready state. The Ready state references four Transition Objects, which identify the allowed state transitions to the Running and Halted states and from the Halted and Ready states.

The Running state indicates that the Program is actively performing its Function. The Running state references five Transition Objects, which identify the allowed state transitions to the Halted, Ready, and Suspended states and from the Ready and Suspended states.

The Suspended state indicates that the Program has stopped performing its Function, but retains the ability to resume the Function at the point at which it was executing when suspended. The Suspended state references four Transition Objects, which identify the allowed state transitions to the Ready, Running, and Halted state and from the Ready state.

ProgramStateMachineType Transitions are instances of the TransitionType defined in OPC 10000-16 which also includes the definitions of the ToState, FromState, HasCause, and HasEffect references used. Table 7 specifies the transitions defined for the ProgramStateMachineType. Each transition is assigned a unique TransitionNumber defined in Table 6.

Table 7 – ProgramStateMachineType Additional References

SourceBrowsePath	Reference Type	Is Forward	TargetBrowsePath
HaltedToReady	ToState	True	Ready
	FromState	True	Halted
	HasCause	True	Reset
	HasEffect	True	ProgramTransitionEventType
	HasEffect	True	AuditProgramTransitionEventType
ReadyToRunning	ToState	True	Running
	FromState	True	Ready
	HasCause	True	Start
	HasEffect	True	ProgramTransitionEventType
	HasEffect	True	AuditProgramTransitionEventType
RunningToHalted	ToState	True	Halted
	FromState	True	Running
	HasCause	True	Halt
	HasEffect	True	ProgramTransitionEventType
	HasEffect	True	AuditProgramTransitionEventType
RunningToReady	ToState	True	Ready
	FromState	True	Running
	HasEffect	True	ProgramTransitionEventType
	HasEffect	True	AuditProgramTransitionEventType
RunningToSuspended	ToState	True	Running
	FromState	True	Suspended
	HasCause	True	Suspend
	HasEffect	True	ProgramTransitionEventType
	HasEffect	True	AuditProgramTransitionEventType
SuspendedToRunning	ToState	True	Running
	FromState	True	Suspended
	HasCause	True	Resume
	HasEffect	True	ProgramTransitionEventType
	HasEffect	True	AuditProgramTransitionEventType
SuspendedToHalted	ToState	True	Halted
	FromState	True	Suspended
	HasCause	True	Halt
	HasEffect	True	ProgramTransitionEventType
	HasEffect	True	AuditProgramTransitionEventType
SuspendedToReady	ToState	True	Ready
	FromState	True	Suspended
	HasCause	True	Reset
	HasEffect	True	ProgramTransitionEventType
	HasEffect	True	AuditProgramTransitionEventType
ReadyToHalted	ToState	True	Halted
	FromState	True	Ready
	HasCause	True	Halt
	HasEffect	True	ProgramTransitionEventType
	HasEffect	True	AuditProgramTransitionEventType

The HaltedToReady transition specifies the transition from the Halted to Ready states. It may be caused by the Reset Method.

The ReadyToRunning transition specifies the transition from the Ready to Running states. It is caused by the Start Method.

The RunningToHalted transition specifies the transition from the Running to Halted states. It is caused by the Halt Method.

The RunningToReady transition specifies the transition from the Running to Ready states. The RunningToSuspended transition specifies the Transition from the Running to Suspended states. It is caused by the Suspend Method.

The SuspendedToRunning transition specifies the transition from the Suspended to Running states. It is caused by the Resume Method.

The SuspendedToHalted transition specifies the transition from the Suspended to Halted states. It is caused by the Halt Method.

The SuspendedToReady transition specifies the transition from the Suspended to Ready states. It is caused internally.

The ReadyToHalted transition specifies the transition from the Ready to Halted states. It is caused by the Halt Method.

Two HasEffect References are specified for each Program transition. These effects are Events of ProgramTransitionEventType and AuditProgramTransitionEventType defined in 5.2.5. The ProgramTransitionEventType notifies Clients of the Program transition and conveys result data. The AuditProgramTransitionEventType is used to audit transitions that result from Program Control Methods.

Figure 6 – ProgramStateMachineType causes and effects