| 摘要 |
PURPOSE:To switch a clock signal without applying any load to a control section by adopting a constitution where a clock switching means selects an internal clock signal autonomously when the supply of an external clock signal is stopped. CONSTITUTION:An internal clock generating means 100 generates an internal clock signal CKi having nearly the same period as that of an external clock signal CKe. A clock monitoring means 200 monitors whether or not the signal CKe is supplied. A clock switching means 300 receives the signals CKe, CKi and when the means 200 decides that the signal CKe is normally supplied, the means 300 selects the signal CKe and when the means 200 decides that the supply of the signal CKe is stopped, the means 300 selects the signal CKi, and the resulting signal is supplied to a digital device. Thus, when the supply of the signal CKe is stopped, the means 300 selects the signal CKi autonomously and the load of the control section managing the control of the digital equipment is prevented. |
