soc的外部中断，可以实现对外部电平的感知，增加了单片机的适应能力-soc external interrupts, can achieve levels of external perception, increased ability to adapt SCM

给程序可以帮助你掌握测量外部晶振频率的测量-This program shows an example of how the internal oscillator can be used to measure the external oscillator frequency.