Data transmission interface and electronic device using the same

1. A data transmission interface, for coupling to an external apparatus, comprising:

a first signal transmission line and a second signal transmission line, for transmitting a differential signal to the external apparatus;

a first resistor and a voltage-variable component, selectively connected to the first signal transmission line; and

a second resistor, connected to the second signal transmission line;

wherein, when the data transmission interface is initially coupled to the external apparatus, the voltage-variable component is connected to the first signal transmission line, and the first signal transmission line presents a first voltage in response to a type of the external apparatus, and

wherein when the type of the external apparatus is determined, the voltage-variable component is disconnected from the first transmission line and the first resistor is connected to the first signal transmission line allowing the data transmission interface to operate in a corresponding state.

2. The data transmission interface of claim 1 , wherein the first voltage has different logic voltage levels when the data transmission interface is coupled to different external apparatus.

3. The data transmission interface of claim 1 , wherein resistance of the voltage-variable component is larger than resistance of the first resistor.

4. The data transmission interface of claim 1 , wherein resistance of the voltage-variable component is configured such that the first signal transmission line has different voltages when the data transmission interface is coupled to different apparatuses.

5. The data transmission interface of claim 1 , wherein the first resistor and the second resistor are boost resistors of the first signal transmission line and the second signal transmission line, respectively.

6. The data transmission interface of claim 1 , wherein the second resistor disconnects from the second signal transmission line in response to the first voltage which is associated with the external apparatus.

7. An electronic device, comprising:

a signal line pair, comprising two signal lines, for transmitting a differential signal to an external apparatus;

a pair of boost resistors, respectively connected to the signal lines of the signal line pair while transmitting the differential signal; and

a voltage-variable component, selectively connected to one of the signal lines of the signal line pair, for assisting in distinguishing a type of the external apparatus when the electronic device is coupled to the external apparatus,

wherein, when the electronic device is initially coupled to the external apparatus, the voltage-variable component is connected to the signal line connected to the voltage-variable component, which presents a first voltage in response to the external apparatus, and

wherein when the type of the external apparatus is distinguished, the voltage-variable component is disconnected from the one of the signal lines of the signal line pair and wherein the boost resistor corresponding to the signal line connected to the voltage-variable component is connected to the signal line connected to the voltage-variable component in response to the first voltage which is associated with the external apparatus, allowing transmission of the differential signal.

8. The electronic device of claim 7 , wherein the first voltage has different logic voltage levels when the data transmission interface is coupled to different external apparatus.

9. The electronic device of claim 7 , wherein resistance of the voltage-variable component is configured such that the signal line connected to the voltage-variable component having different voltage when the electronic device is coupled to different apparatuses.

10. The electronic device of claim 7 , wherein the boost resistor corresponding to the signal line disconnected from the voltage-variable component selectively disconnects from the signal line disconnected from the voltage-variable component in response to the first voltage which is associated with the external apparatus.

11. The electronic device of claim 7 , wherein the resistance of the voltage-variable component is larger than that of the boost resistor disposed on the signal line connected to the voltage-variable component.

12. A data transmission method, comprising:

transmitting, to an external apparatus, a differential signal via a data transmission interface, comprising a first signal transmission line and a second signal transmission line;

connecting a voltage-variable component to the first signal transmission line while the data transmission interface is initially coupled to the external apparatus, wherein the first signal transmission line presents a first voltage in response to a type of the apparatus; and

connecting the first signal transmission line to a first resistor while disconnecting the first signal transmission line from the voltage-variable component, after the first voltage is present on the first signal transmission line.

13. The method for data transmission of claim 9 , wherein the resistance of the voltage-variable component is larger than that of the first resistor.

14. The method for data transmission of claim 9 , further comprising:

setting the resistance of the voltage-variable component such that the first signal transmission line having different voltages while the data transmission interface is coupled to different devices.

15. The method for data transmission of claim 9 , wherein the first resistor is a boost resistor of the first signal transmission line.

16. The method for data transmission of claim 9 , wherein the second signal transmission line disconnects from a boost resistor after the corresponding voltage is presented on the first signal transmission.