you should look into the datasheet for your device.it typically specify the maximum current through the clamping diodes. Usually that's 20 - 25ma: anything greater than that can cause permanent damage to the clamping diodes.
so at 5v, the minimum resistance allowed is 5v/20ma = ...
If you are doing adc on that pin,you will look into the maximum resistance specification.
if you are applying an ac signal to it, you need to look into the input capacitance figure to make sure that the resistance isn't too large for your signal (as the resistance forms a low-pass filter with the pin's input capacitance).
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接上拉还怎么判断高电平呢?上啦之后不是出了IO口上的电平非常低，就一直显示高电平吗？
正确的应该是IO口10K下拉接地，然后要检测的信号线直接接IO口吧，这样只有电平为高时，IO口才会显示高电平吧.
请大家鉴定……
so at 5v, the minimum resistance allowed is 5v/20ma = ...
If you are doing adc on that pin,you will look into the maximum resistance specification.
if you are applying an ac signal to it, you need to look into the input capacitance figure to make sure that the resistance isn't too large for your signal (as the resistance forms a low-pass filter with the pin's input capacitance).
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