我用KL25开发板遇到了一个问题：我连接板上的USBDM口时电源灯不亮，我用万用表测量了下板上只有2.2V下载程序的时候也下载不了，我尝试了 Flash Programmmer -ARM 解锁 但是在解锁的时候还是不成功。---------------------------
USBDM - Target Connection Failure
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Connection with the target has failed.

Please cycle power to the target.

Retry connection?
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是(Y)   否(N)   
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Programming Error
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Programming of the target flash failed!

Reason: BDM has no connection to target
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确定   
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出现了这样的错误要怎么解决呀！十分火急 求帮忙啊！在此谢谢了！！