| 摘要 |
<p>PURPOSE:To detect the actual frequency of the clock of a CPU by providing a frequency comparing part and comparing the oscillation frequency of a quartz oscillator given to the CPU with a reference frequency. CONSTITUTION:A selector 6 performs switching between outputs of quartz A 71 and quartz B 72, and the output of the selector 6 is given to a CPU 1 as a CPU clock 8. A frequency comparing circuit 12 compares the frequency of a reference clock 13 with that of the CPU clock 8 given to the CPU 1 and outputs a frequency value 14. Thus, the actual operating frequency of the CPU 1 is detected. Since the value of a software timer is properly changed in case of replacement of quartz in an examination process or the like or the change of the oscillation frequency due to trouble of the oscillating frequency, error does not occur.</p> |
