Method and apparatus for sharing an input/output terminal by multiple compensation circuits

1. A method comprising:

selectively enabling each of a first compensation circuit and a second compensation circuit during respective first and second time periods to control a voltage on a shared input/output terminal of an integrated circuit to be substantially equal to a first and second reference voltage respectively utilized by the first and second compensation circuits.

2. The method as recited in claim 1 further comprising selectively enabling at least a third compensation circuit during a third time period to control a voltage on the shared input/output terminal of the integrated circuit to be substantially equal to a third reference voltage utilized by the third compensation circuit.

3. The method as recited in claim 2 wherein only one compensation circuit is enabled at a time.

4. The method as recited in claim 1 further comprising coupling a first power supply node through an external resistor to the input/output terminal.

5. The method as recited in claim 1 further comprising:

during the first time period comparing the voltage on the input/output terminal to the first reference voltage and compensating the voltage on the input/output terminal using a first plurality of transistors of the first compensation circuit according to the comparison; and

during the second time period comparing the voltage on the input/output terminal to the second reference voltage and compensating the voltage on the input/output terminal using a second plurality of transistors of the second compensation circuit according to the comparison.

6. The method as recited in claim 1 further comprising periodically enabling the first and second compensation circuits.

7. The method as recited in claim 1 further comprising turning off a first plurality of transistors of the first compensation circuit during the second time period while the second compensation circuit is enabled and turning off a second plurality of transistors of the second compensation circuit during the first time period while the first compensation circuit is enabled.

8. The method as recited in claim 1 wherein the first and second reference voltages are the same reference voltage.

9. An integrated circuit comprising:

a first and a second compensation circuit coupled to a shared input/output terminal of the integrated circuit and coupled to utilize respectively a first and second reference voltage; and

a selector control circuit coupled to selectively enable each of the first and second compensation circuits at respective first and second time periods to control a voltage on the shared input/output terminal to be substantially equal to, respectively, the first and second reference voltages.

10. The integrated circuit as recited in claim 9 further comprising:

one or more additional compensation circuits coupled to the shared input/output terminal, the selector circuit controlling all the compensation circuits such that only one compensation circuit is enabled at any one time to control the voltage on the shared input/output terminal to be substantially equal to a reference voltage utilized by the one compensation circuit that is enabled.

11. The integrated circuit as recited in claim 9 further comprising:

a first plurality of transistors of the first compensation circuit selectively controlled to adjust the voltage on the input/output terminal during the first time period in accordance with a comparison of the voltage on the input/output terminal to the first reference voltage; and

a second plurality of transistors of the second compensation circuit selectively controlled to adjust the voltage on the input/output terminal during the second time period in accordance with a comparison of the voltage on the input/output terminal to the second reference voltage.

12. The integrated circuit as recited in claim 9 wherein the first and second compensation circuits are periodically enabled.

13. The integrated circuit as in claim 11 wherein further comprising turning off a first plurality of transistors of the first compensation circuit during the second time period while the second compensation circuit is enabled and turning off a second plurality of transistors of the second compensation circuit during the first time period while the first compensation circuit is enabled.

14. The integrated circuit as in claim 11 wherein the first and second reference voltages are the same reference voltage.

15. A method comprising:

enabling a first compensation circuit during a first period, while a second compensation circuit is disabled, to compare a reference voltage to a voltage present on an input/output terminal of an integrated circuit and to adjust operation of the first compensation circuit in response to the comparison by selectively enabling transistors coupling the input/output terminal to a power supply node to cause the reference voltage and the voltage on the input/output terminal to be substantially the same and storing compensation settings corresponding thereto in a storage; and

enabling a second compensation circuit during a second time period, while the first compensation circuit is disabled, to compare a reference voltage to a voltage on the input/output terminal and to adjust operation of the second compensation circuit in response to the comparison.

16. The method as recited in claim 15 further comprising coupling a first power supply node through an external resistor to the input/output terminal.

17. The method as recited in claim 15 further comprising periodically enabling the first and second compensation circuits using one or more counters.

18. The method as recited in claim 15 further comprising turning off a first plurality of transistors in the first compensation circuit coupling the input/output terminal to a power supply node during the second time period while the second compensation circuit is enabled and turning off a second plurality of transistors of the second compensation circuit during the first time period while the first compensation circuit is enabled.

19. An apparatus comprising:

an integrated circuit including,

a plurality of compensation circuits coupled to vary respective resistances of the compensation circuits to thereby control a current received from an external source through a terminal of the integrated circuit, the current being supplied at a voltage determined by one or more reference voltages respectively supplied to the compensation circuits;

a compensation select circuit coupled to selectively enable each of the compensation circuits to control the current through the terminal at different times; and

a storage to store compensation values for the compensation circuits.

20. The apparatus as recited in claim 1 further comprising a resistor, external to the integrated circuit coupled to the input/output terminal, the resistor being coupled to a supply voltage.

21. A method comprising:

during a first time period enabling a first compensation circuit to determine first compensation settings to control a voltage on a terminal of an integrated circuit to be substantially equal to a first reference voltage;

storing the first compensation settings in a storage;

during a second time period while the first compensation circuit is disabled, enabling a second compensation circuit to determine second compensation settings to control the voltage on the terminal of the integrated circuit to be substantially equal to a second reference voltage; and

during the second time period, supplying the first compensation settings to one or more output drivers driving one or more output terminals.

22. The method as recited in claim 1 further comprising storing compensation settings used to control the voltage in a storage.

23. The method as recited in claim 1 further comprising supplying the compensation settings determined by one of the first and second compensation settings to one or more input/output circuits while the one of the first and second compensation circuits is off.

24. The method as recited in claim 15 further comprising supplying the stored compensation settings while the first compensation circuit is off to one or more output drivers.

25. The apparatus as recited in claim 9 further comprising storage to store compensation values to control the voltage on the shared input/output terminal to be substantially equal to the first and second reference voltages.