Patent ID: 8427392

Claim:
A notebook computer having an display port capable of outputting a first signal and a second signal to an external display device to display an image, the notebook computer comprising: a monitor device built in the notebook computer; an embedded controller capable of outputting an enable signal; and a detecting circuit receiving the first signal and the second signal, the detecting circuit comprising: a first transistor, wherein the source of the first transistor is connected to a power supply voltage, and the gate of the first transistor receives the enable signal; a first resistor having two ends, wherein one end of the two ends receives the second signal; and a comparator, wherein the positive input of the comparator receives the second signal, the negative input of the comparator receives a reference voltage, the comparator receives the enable signal and is actuated according to the enable signal, and the output of the comparator is capable of outputting a interrupt request signal, wherein when the external display device is disconnected with the display port, the detecting circuit is capable of determining the voltage level of the second signal according to the actuation of the enable signal at a blanking interval of the first signal to generate an interrupt request signal and switch the image to the monitor device automatically.