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你好，芯片手册上是这样介绍的：
All GPIO pins are I/O/Z and have an internal
pullup, which can be selectively enabled or disabled on a per-pin basis. This feature only applies to the
GPIO pins. The pullups are not enabled at reset.
但是如果你的应用对初始状态要求很高（必须低电平或者高电平的话），建议还是加一个外部的上下拉，确保不会有意外发生。
