| 摘要 |
<p>PROBLEM TO BE SOLVED: To promote the high-accuracy start of program processing by a CPU by shortening the stable oscillation time of crystal oscillation circuit by providing a self-exciting oscillation circuit, and confirming the stability of oscillation by counting clocks. SOLUTION: Just after a power supply voltage is turned on, a clock signal outputted from a self-exciting oscillation circuit 3 is used as a clock supply means for the CPU and supplied through a gate 13 to a crystal oscillation circuit 2, and stable crystal oscillation time is shortened. Besides, this clock signal is counted by a timer 6. At the time point of count value 8, an FF 8 is set, the gate 13 is closed, and a timer 5 starts counting outputs from the crystal oscillation circuit 2. When the count value of the timer 6 is '15' and the count value of the timer 5 is from '6' to '7', a discrimination circuit 10 judges that the operation of crystal oscillation circuit 2 is stabilized, an FF 11 is set, and a clock switching circuit 12 switches the clock from the self- exciting oscillation circuit 3 up to the moment to a clock signal from the crystal oscillation circuit 2.</p> |
