Patent ID: 7135939

Claim:
A semiconductor device, comprising: an external oscillation circuit connected with an external resonator and generating a first clock signal; a self-exciting circuit generating a second clock signal; a monitoring circuit monitoring an oscillation state of said external resonator using said second clock signal and outputting a terminating signal of waiting time for stabilization of oscillation; and a first register having a capability of establishing a period of time until outputting said terminating signal of the waiting time for stabilization of oscillation, which is rewritable; and a second register in which a fixed value corresponding to a minimum elapsed time among settable values in said first register is established, wherein when judged that the oscillation state of said external resonator is established before passage of time corresponding to the value established in said first register, said monitoring circuit outputs said terminating signal of waiting time for stabilization of oscillation after passage of the minimum time based on the value established in said second register.