5.5.2. REQUEST MODE OPERATION

When a device is in REQUEST mode, we can obtain an input value by calling the appropriate REQUEST <input class> function. The actions caused by calling this function are:

• a) Creation of an evaluation process for the specified device and assignment of its value to the initial value taken from the workstation state list. Echo is carried out by the evaluation process if the echo is ON for the device specified.
• b) The device identifier is added to the list of receivers of its trigger. If this list was previously empty, the validation process is activated.
• c) GPHIGS is suspended until the trigger of the specified device is fired, or until the operator generates an interrupt.
• d) If the trigger is fired, the input value is assigned to the current state of the evaluation process.
• e) Destruction of the evaluation process.
• f) The device identifier is deleted from the list of receivers of its trigger. If the list becomes empty, the validation process is destroyed.
• g) If the trigger is fired, the OK state is sent, otherwise the NONE state is sent.