Patent ID: 8804750

Claim:
A field device performing a communication through a communication line, the field device comprising: first circuits involved with a smart communication; second circuits involved with a fieldbus communication; a token detecting circuit that detects a token corresponding to a frame for the fieldbus communication; a power supply for selectively providing power to the first circuits and the second circuits; a control circuit coupled to the first circuits, the second circuits and the token detecting circuit, respectively, the control circuit: i) causing the power from the power supply to be selectively provided to the second circuits and thereby causing the second circuits to operate and to prevent power from the power supply from being provided to the first circuits, when the token is detected within a given time by the token detecting circuit; and ii) causing the power from the power supply to be selectively provided to the first circuits and thereby cause the first circuits to operate and to prevent power from the power supply from being provided to the first circuits and thereby causing the second circuits not to operate when the token is not detected within the given time by the token detecting circuit or when a frame for the smart communication is detected within the given time by the token detecting circuit.