Buffer circuit

1. A buffer circuit capable of switching between an input mode and an output mode, said buffer circuit comprising:

a first transistor for outputting a prescribed voltage to an input/output terminal depending on a conductive state during the output mode of the buffer circuit, in accordance with a data signal to be output from said input/output terminal;

a pre-driver for controlling the conductive state of the first transistor during the output mode of the buffer circuit, in accordance with said data signal; and

a power supply circuit for providing a first power supply to the pre-driver during the output mode of the buffer circuit and providing or blocking the first power supply to the pre-driver in accordance with an input voltage to the input/output terminal during the input mode of the buffer circuit.

2. The buffer circuit according to claim 1 , wherein, if the input voltage to the input/output terminal is higher than the first power supply, the input voltage to the input/output terminal is provided to a control terminal of the first transistor.

3. The buffer circuit according to claim 1 , wherein the input voltage to the input/output terminal is provided to the control terminal of the first transistor through a gate controller placed between the input/output terminal and the control terminal of the first transistor.

4. The buffer circuit according to claim 1 , wherein the input/output terminal is commonly used for both the input mode and the output mode of the buffer circuit.

5. The buffer circuit according to claim 1 , further comprising:

an N-well controller for controlling a voltage of an N-well area where a plurality of PMOS transistors are formed.

6. The buffer circuit according to claim 1 , wherein the power supply circuit includes a power supply voltage switch and determines to provide or block the first power supply to the pre-driver depending on a conductive state of the power supply voltage switch.

7. A buffer circuit connected to an input/output terminal of a semiconductor apparatus, comprising:

a first transistor for outputting a prescribed voltage to said input/output terminal depending on a conductive state, in accordance with a data signal to be output from said input/output terminal during an output mode of said buffer circuit;

a pre-driver for controlling the conductive state of the first transistor in accordance with said data signal; and

a power supply circuit for providing or blocking a first power supply to the pre-driver in accordance with an input voltage to the input/output terminal during an input mode of said buffer circuit.

8. The buffer circuit according to claim 7 , wherein, if the input voltage to the input/output terminal is higher than the first power supply, the input voltage to the input/output terminal is provided to a control terminal of the first transistor.

9. The buffer circuit according to claim 7 , wherein the input voltage to the input/output terminal is provided to the control terminal of the first transistor through a gate controller placed between the input/output terminal and the control terminal of the first transistor.

10. The buffer circuit according to claim 7 , wherein the input/output terminal is commonly used for both an input mode and an output mode of the buffer circuit.

11. The buffer circuit according to claim 7 , further comprising:

an N-well controller for controlling a voltage of an N-well area where a plurality of PMOS transistors are formed.

12. The buffer circuit according to claim 7 , wherein the power supply circuit includes a power supply voltage switch and determines to provide or block the first power supply to the pre-driver depending on a conductive state of the power supply voltage switch.

13. A buffer circuit capable of switching between an input mode and an output mode, said buffer circuit comprising:

a first transistor for outputting a prescribed voltage to an input/output terminal depending on a conductive state during the output mode of the buffer circuit, in accordance with a data signal to be output during the output mode;

a pre-driver for controlling the conductive state of the first transistor during the output mode of the buffer circuit, in accordance with said data signal to be output; and

a power supply circuit for providing a first power supply to the pre-driver during the output mode of the buffer circuit, and, in accordance with an input voltage to the input/output terminal, selecting either one of the first power supply or the input voltage and providing a power supply to the pre-driver during the input mode of the buffer circuit.

14. The buffer circuit according to claim 13 , wherein, if the input voltage to the input/output terminal is higher than the first power supply, the input voltage to the input/output terminal is provided to a control terminal of the first transistor.

15. The buffer circuit according to claim 13 , wherein the input voltage to the input/output terminal is provided to the control terminal of the first transistor through a gate controller placed between the input/output terminal and the control terminal of the first transistor.

16. The buffer circuit according to claim 13 , wherein the input/output terminal is commonly used for both the input mode and the output mode of the buffer circuit.

17. The buffer circuit according to claim 13 , further comprising:

an N-well controller for controlling a voltage of an N-well area where a plurality of PMOS transistors are formed.

18. The buffer circuit according to claim 13 , wherein the power supply circuit includes a power supply voltage switch for providing the first power supply to the pre-driver, and an input/output terminal voltage transfer for providing the voltage at the input/output terminal to the pre-driver, and if the voltage at the input/output terminal is lower than the first power supply, the power supply voltage switch becomes conductive and, if the voltage at the input/output terminal is higher than the first power supply, the input/output terminal voltage transfer becomes conductive.

19. The buffer circuit according to claim 18 , wherein the power supply voltage switch is controlled to become conductive by a supply controller and controlled to become nonconductive by a cutoff controller in accordance with the voltage at the input/output terminal.

20. The buffer circuit according to claim 18 , wherein the input/output terminal voltage transfer becomes conductive in accordance with the voltage at the input/output terminal.