HDMI apparatus of high-definition TV has switching circuit that outputs low-level/ground potential to second pin of HDMI connector if a first signal is not outputted

1. An electronic device, comprising

a connector to which an external device is connected via a signal cable and that includes at least first and second pins, a predetermined voltage being supplied from the external device to the first pin;

an integrated circuit (IC) that includes a communicator to which a signal is input from the external device via a pin other than the first and second pins of the connector and that outputs, when the communicator is in an activated state, a first signal that indicates that the communicator is in the activated state; and

a switch circuit that outputs to the external device via the second pin, when the first signal has not been outputted by the integrated circuit in a state in which the predetermined voltage is supplied from the external device to the first pin, a first detection signal indicating that a connection of the communicator has not been established with the external device.

2. The electronic device according to claim 1 , wherein the switch circuit outputs, when the first signal has not been output, a low level or a ground potential as the first detection signal.

3. The electronic device according to claim 2 , wherein the switch circuit includes a switch to which the first signal is input as a control signal and that sets the second pin to the low level or the ground potential during a period where the first signal is not input.

4. The electronic device according to claim 3 , wherein the switch includes first to third resistive elements, a MOSFET, and a transistor,

wherein an emitter of the transistor and a source of the MOSFET are grounded,

wherein one end of the first resistive element is connected to one end of the second resistive element, and connected to the first pin of the connector,

wherein another end of the first resistive element is connected to a drain of the MOSFET, and connected to the second pin of the connector,

wherein another end of the second resistive element is connected to a gate of the MOSFET, and connected to a collector of the transistor,

wherein the first signal is supplied to a base of the transistor via the third resistive element,

wherein, during a period where the first signal is not output, the transistor is turned OFF while the MOSFET is turned ON, and

wherein, during a period where the first signal is output, the transistor is turned ON while the MOSFET is turned OFF.

5. The electronic device according to claim 3 , wherein the switch includes a resistive element and a switch element,

wherein the switch element includes first to third terminals, the first terminal being connected to the first pin of the connector, the second terminal being grounded, and the third terminal being connected to the second pin of the connector via the resistive element,

wherein, during a period where the first signal is output, the first and third terminals of the switch element are connected, and

wherein, during the period where the first signal is not output, the second and third terminals of the switch element are connected.

6. The electronic device according to claim 1 , wherein the switch circuit outputs, when the first signal has not been outputted by the integrated circuit, the first detection signal by setting the second pin in an electrically open state.

7. The electronic device according to claim 6 , wherein the switch circuit sets, when the first signal has not been outputted by the integrated circuit, the electrically open state between the first pin and the second pin.

8. The electronic device according to claim 7 , wherein the switch circuit includes a switch to which the first signal is input as a control signal and a resistive element,

wherein the first pin is connected to one end of the switch via the resistive element, and the second pin is connected to another end of the switch, and

wherein the switch sets the electrically open state between the first pin and the second pin during a period where the first signal is not output.

9. The electronic device according to claim 7 , wherein the switch circuit includes a relay to which the first signal is input as a control signal and first and second resistive elements,

wherein the first pin is connected to one terminal of the relay via the first resistive element, and the second pin is connected to a terminal of another end of the relay, and

wherein the relay sets the electrically open state between the first pin and the second pin during a period where the first signal is not output.

10. The electronic device according to claim 7 , wherein the switch includes a resistive element and a switch element,

wherein one end of the resistive element is connected to the first pin of the connector, and another end of the resistive element is connected to the second pin of the connector via the switch element,

wherein, during a period where the first signal is output, the switch element is turned ON, and

wherein, during the period where the first signal is not output, the switch element is turned OFF.

11. The electronic device according to claim 1 , wherein, when the first signal has been outputted by the integrated circuit, the switch circuit outputs to the external device, via the second pin, a second detection signal indicating that a connection of the communicator has been established with the external device.

12. The electronic device according to claim 11 , wherein, during a period where the first signal is output, the switch circuit outputs the signal of the predetermined voltage supplied to the first pin as the second detection signal from the second pin.

13. The electronic device according to claim 1 , further comprising a nonvolatile memory that stores identification data indicating a resolution and a format of a video/audio signal,

wherein the connector further includes a pin by which the external device reads the identification data from the nonvolatile memory.

14. The electronic device according to claim 1 , wherein the control units stores identification data indicating a resolution and a format of a video/audio signal, and

wherein the connector further includes a pin by which the external device accesses the control unit to acquire the identification data.

15. The electronic device according to claim 1 , wherein the activated state of the communicator includes a power-ON state of the communicator.

16. The electronic device according to claim 1 , wherein the activated state of the communicator includes an initialization-completed state of the communicator.

17. A communication system, comprising:

a sink device that includes the electronic device according to claim 1 ; and

a source device that includes the external device to which the sink device is connected to via a communication cable that includes the signal cable,

wherein the source device supplies the predetermined voltage to the sink device, and recognizes, when receiving a detection signal of the predetermined voltage from the sink device, that it is connected to the sink device.

18. A hot-plug control method implemented in an electronic device that includes a connector to which an external device is connected via a signal cable and that includes at least first and second pins, a predetermined voltage being supplied from the external device to the first pin, the method comprising:

when a communicator, to which a signal is inputted from the external device via a pin other than the first and second pins of the connector, is activated, outputting a first signal that indicates that the communicator is in the activated state; and

outputting to the external device, via the second pin, when the first signal has not been outputted in a state in which the predetermined voltage is supplied from the external device to the first pin, a first detection signal indicating that a connection of the communicator has not been established with the external device.

19. The electronic device according to claim 1 , wherein, when the first signal has not been outputted by the integrated circuit, the communicator is not in the activated state.

20. The electronic device according to claim 1 , wherein, based on the first detection signal, when the external device recognizes that it is not connected to the electronic device, the external device does not carry out an access operation to access the electronic device.

21. The hot-plug control method according to claim 18 , further comprising:

when the predetermined voltage has been supplied from the external device to the first pin, in the state where the communicator is activated, outputting to the external device, via the second pin, a signal of the predetermined voltage supplied to the first pin as a second detection signal.