Semiconductor device capable of selecting operation mode based on clock frequency

摘要

A semiconductor device which operates in synchronism with a first clock externally provided. The semiconductor device includes a clock-generation circuit generating a second clock which maintains a predetermined phase relation with the first clock, a check circuit for checking a frequency of the first clock based on at least one internal signal generated by the clock-generation circuit, and an internal circuit which switches an operation mode according to results of the checking.