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Kinetis KV10Z32xx7 self lock problems

Question asked by Zhitai Liu on Apr 17, 2017
Latest reply on Apr 18, 2017 by Hui_Ma

Hi, first time design with NXP/Fressscale mcu. In the beginning, I use FRDM KV10Z to develop firmware, it goes pretty well. However, when I first time using my custom PCB with 32 pin LQFP kv10Z32vlc7, sometime the mcu locks himself accidentally! I am using J-Link and KEIL uVsition. Sometime it goes well, but very often my Jlink cannot connect with the mcu and having the following msg:

Once jLink shows these message, I cannot unsecure this mcu anymore, I have to desolder it and replace by a new one. 

I've tried about 10 pcs, now there are 4 of them got locked!

Please help me here. I've spent few days on this, and getting frustrating.

 

NOTE:

1 Jlink is connected to MCU through SWD_CLK, SWD_IO, Gnd, VCC. Reset_b pin and NMI_b pins are pulled high externally. 

2 I noticed that when the reset_b pin is not pulled high (left open), it goes low by itself. This is quit strange. 

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