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您好,那您的问题是使用一段时间之后,下行端口本来是能识别USB3.0的,后来不行了,只能识别USB2.0对吧?
然后测试发现, 下行端口插上USB3.0的器件,24Mhz的晶振不起振,但是插USB2.0的话,是可以正常起振的是吗?
如果是这样的话,要检查下晶振的稳定性,负载电容的范围,频率的tolerance,以及晶振的等效电阻等是否都满足要求。
参考数据手册8.3.5 Crystal Requirements的介绍。