As described in the introduction, the two parts of the control unit and vs | plus work closely together. The device determines the operating states that are currently valid. The following states are important for vs | plus:
- Initialise: When the control unit is put into operation, the vs | plus internal values must be initialised.
- Switch on: When vs | plus is to start controlling the intersection for the first time, the control device informs vs | plus of this. This occurs when a switch-on sequence has been processed or when the device is to switch from a fixed time plan to traffic dependency. At this moment, vs | plus takes over the current states of the signal groups and detectors in order to be able to continue working with them. Only partial nodes can also be switched on.
- Normal operation: In this operating state, vs | plus works according to the parameters that are supplied.
- Out of service: This is the opposite state to the previous one. vs | plus must not switch the signals. These are defined by a fixed time or the off state. The device has control of the outputs. vs | plus continues to work in the background and registers all signals from both the IT and the PT. However, no signals are switched. If the control device switches back to normal mode, all requests not taken into account are processed. This means that if a bus makes a request and it is switched to vs | plus, this request is not lost but is taken into account in vs | plus.
- Switching to or off: When changing programmes (switching to) or switching off, vs | plus must also complete certain tasks before the device can take control of the signals. Switching from one vs | plus programme to another vs | plus programme can be done immediately. For vs | plus, a programme change is in most cases only a change of parameters. This change can be handled by vs | plus without any problems. When switching to a switch-off pattern or to a fixed time plan, vs | plus must adapt the current state of the signals to the requirements of the switch-to plan or the fixed time plan before switching. As vs | plus does not have access to the required information, the control device transfers the status of the signals to vs | plus when it requests this operating state. The task for vs | plus is now to switch from the current state of the signals to the requested new state. Once this has taken place, vs | plus signals to the control device that the target state has been reached and this then takes over the switching sovereignty of the signals. Only partial nodes can also be switched off.