Modes are special kind of states: they are states of which the operators must be aware. They are elements of the operational scenario.

Example

The Caps Lock key on a PC enables the operators to select a mode according to their intention to type either lower case or upper case letters.

Mode control

Like all states, they are arranged in mode sets, and controlled by state machines. The special features are exemplified in the simple reactive system ... Modes can be controls in various ways.

• They can be selected by the operators, using selectors, representing the operator's intention. They are set by operational controls, such as switches and buttons. In the Caps Lock example, it is the set of {Lower case, Upper case}
• They can be set automatically, by input from special sensors, or special software, such as in response to measurements crossing thresholds,
• They can be changed interactively, when following certain operational procedures. Examples are the primary modes. Examples of routine modes are those used for enabling production, maintenance, troubleshooting, testing or training. An example of exceptional modes is the human-machine mode control in emergency.

Counter example

An example of a state-set which is not a mode-set is any state machine used internally in special algorithms, of no significance to the operator's awareness.

Updated on 03 Jun 2017.