如图示,是一个测U1大小的电路,由P2.0给C充电的同时,定时器开始计时,充到U1时,计时停止,通过这个时间就能得出U1.
我想问的问题是,这里的R2的作用是什么?起作用的原理是什么?什么情况下可以不要,什么情况下要,为什么? 谢谢!!!
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