This mode sets up the synchronous environment between the application and a given device. In this mode a given device is inactive until the application explicitly requests input from it by calling the REQUEST <input_class> function. This function waits for a value from the specified input device which must be in REQUEST mode.
During the request, the device is activated and the application waits until the operator supplies input using some type of trigger, or until he generates an interrupt. The interrupt (break) and the trigger depend on the input device used. If the operator generates an interrupt (break), the input value is invalid.