| 摘要 |
The apparatus comprises a counter to count the pulse signal of a frequency proportional to the rotation speed of the motor. The apparatus further comprises a presettable down-counter which counts down to a predetermined value sequentially in response to clock pulses, and a CPU for reading out the count value of the first counter upon completion of prescribed count-down of the presettable down-counter. The rotation speed of the motor is them calculated on the basis of the count value read out. The CPU changes the count value of the presettable down-counter back to the predetermined value when the calculation is completed.
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