Radio-controlled wristwatch

1. A radio-controlled wristwatch, comprising:

reception means for receiving a radio wave from a satellite and extracting day-related information therefrom;

timekeeping-circuit halting means for halting an operation of a timekeeping circuit based on a power supply voltage;

timekeeping-circuit halt detection means for detecting that the operation of the timekeeping circuit has been halted by the timekeeping-circuit halting means;

a nonvolatile memory for storing the day-related information and a cycle number of the day-related information; and

cycle-number updating means for comparing, when the timekeeping-circuit halt detection means detects that the operation of the timekeeping circuit has been halted, the day-related information extracted by the reception means and the day-related information stored in the nonvolatile memory to each other, and updating the cycle number of the day-related information when the day-related information stored in the nonvolatile memory is larger than the day-related information extracted by the reception means.

2. The radio-controlled wristwatch according to claim 1 , wherein the cycle-number updating means updates the cycle number of the day-related information when a difference between the day-related information stored in the nonvolatile memory and the day-related information extracted by the reception means is equal to or larger than a predefined value, and inhibits the cycle number of the day-related information from being updated when the difference is smaller than the predefined value.

3. The radio-controlled wristwatch according to claim 1 , further comprising nonvolatile memory writing means for sensing a time to update the day-related information and the cycle number of the day-related information based on timekeeping performed by the timekeeping circuit, and writing the day-related information and the cycle number of the day-related information, which have been updated, to the nonvolatile memory.

4. The radio-controlled wristwatch according to claim 3 , further comprising write inhibition means for inhibiting the nonvolatile memory writing means from writing to the nonvolatile memory in a case where a possibility that writing performed by the nonvolatile memory writing means fails is sensed.

5. The radio-controlled wristwatch according to claim 4 , wherein the write inhibition means postpones the writing to the nonvolatile memory performed by the nonvolatile memory writing means in the case where the possibility that the writing fails is sensed, and permits the writing to the nonvolatile memory performed by the nonvolatile memory writing means in a case where the possibility that the writing fails has disappeared.

6. The radio-controlled wristwatch according to claim 4 , wherein the case where the possibility that the writing fails is sensed comprises at least one of reduction in the power supply voltage, reception of the radio wave from the satellite performed by the reception means, driving of a day wheel, fast-forwarding of a hand, driving of an additional function, and a standby state for the reception of the radio wave from the satellite performed by the reception means.

7. The radio-controlled wristwatch according to claim 1 , wherein the reception means receives information relating to a leap second at a time predicted by referring to the cycle number of the day-related information.

8. The radio-controlled wristwatch according to claim 2 , further comprising nonvolatile memory writing means for sensing a time to update the day-related information and the cycle number of the day-related information based on timekeeping performed by the timekeeping circuit, and writing the day-related information and the cycle number of the day-related information, which have been updated, to the nonvolatile memory.

9. The radio-controlled wristwatch according to claim 8 , further comprising write inhibition means for inhibiting the nonvolatile memory writing means from writing to the nonvolatile memory in a case where a possibility that writing performed by the nonvolatile memory writing means fails is sensed.

10. The radio-controlled wristwatch according to claim 9 , wherein the write inhibition means postpones the writing to the nonvolatile memory performed by the nonvolatile memory writing means in the case where the possibility that the writing fails is sensed, and permits the writing to the nonvolatile memory performed by the nonvolatile memory writing means in a case where the possibility that the writing fails has disappeared.

11. The radio-controlled wristwatch according to claim 5 , wherein the case where the possibility that the writing fails is sensed comprises at least one of reduction in the power supply voltage, reception of the radio wave from the satellite performed by the reception means, driving of a day wheel, fast-forwarding of a hand, driving of an additional function, and a standby state for the reception of the radio wave from the satellite performed by the reception means.

12. The radio-controlled wristwatch according to claim 9 , wherein the case where the possibility that the writing fails is sensed comprises at least one of reduction in the power supply voltage, reception of the radio wave from the satellite performed by the reception means, driving of a day wheel, fast-forwarding of a hand, driving of an additional function, and a standby state for the reception of the radio wave from the satellite performed by the reception means.

13. The radio-controlled wristwatch according to claim 10 , wherein the case where the possibility that the writing fails is sensed comprises at least one of reduction in the power supply voltage, reception of the radio wave from the satellite performed by the reception means, driving of a day wheel, fast-forwarding of a hand, driving of an additional function, and a standby state for the reception of the radio wave from the satellite performed by the reception means.