| 摘要 |
PROBLEM TO BE SOLVED: To enable abnormality detection even when a sub-oscillation circuit stops and also achieve the miniaturization of an oscillation circuit itself .SOLUTION: In a period predetermined in accordance with the oscillation frequency of a sub-oscillation circuit 50, the lower limit value and upper limit value of the number of high speed clocks of a main oscillation circuit 30 are preliminarily stored in a lower limit value register 40 and an upper limit value register 44. In a first abnormality detection part 22, high speed clocks are counted by a counter 32 in a period corresponding to a high speed clock and a low speed clock, and the count value is compared with the upper limit value by a comparator 42, and when the count value exceeds the upper limit value, abnormality is detected, and the output value of a register 36 corresponding to the count value is compared with the lower limit value by a comparator 38, and when the output value is less than the lower limit value, abnormality is detected. In a second abnormality detection part 24, when the respective bits of the output value of a shift register 54 which has fetched a frequency-division clock obtained by frequency-dividing the high speed clock by a frequency-divider 52 in a timing corresponding to the low speed clock are all the same value, abnormality is detected by an oscillation confirmation circuit 56. |
