| 摘要 |
PROBLEM TO BE SOLVED: To prevent ear-offensive noise from being superposed on a buzzer sound. SOLUTION: When frequency-division ratio data are written to a counter/ timer register 530, a counter/timer circuit 534 divides the frequency of the oscillation signal of an oscillation circuit by the value indicated by the frequency- division ratio data. When output acknowledgement data are written to a port-B register 536, an envelope generating circuit 538 outputs a variable gain control signal. The variable gain control circuit 540 varies the amplitude of a frequency- division signal by a value corresponding to the voltage of the variable gain control signal. When output stop data are written to the port-B register 536, the envelope generating circuit 538 does not output the variable gain control signal any more. The variable gain control circuit 540 stops amplitude control over the frequency-division signal.
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