下图所示的简单电路可在内部和外部时钟源之间进行自动选择而不需要开关或其它任何输入信号。如果有外部时钟信号,电路则自动选择该信号源,反之电路选择内部时钟源。在实验室的测试设备中,该电路证明是有一定价值的,它能提供一种产生既简单又经济的时钟输入信号的方法。该电路还可应用于那些具有能消除人为误差的自动选择时钟源功能的复杂装置中。 The simple circuit shown below can be automatically selected between internal and external clock sources without the need for a switch or any other input signal. If there is an external clock signal, the circuit automatically selects the source, whereas the circuit selects the internal clock source. This circuit proves to be of some value in laboratory test equipment and provides a way to produce a simple and economical clock input signal. The circuit can also be used in complex devices that have the ability to automatically select a clock source that eliminates human error.