AnsweredAssumed Answered

K21 hangs when going from low power to high gain crystal mode

Question asked by Phuc Le Dinh on Dec 1, 2015
Latest reply on Dec 6, 2015 by Hui_Ma

Hi all,


Need a little help here.


I'm using K21FN1M0A on one of my custom design. My firmware consists of a bootloader and the actual firmware. I want to run my board in high gain crystal mode (I'm aware that a 1M Ohm resistor needs to be added). Here is the clock description of each piece of software:


Bootloader: use low power crystal mode

Firmware: Use high gain




1 - When I configured my firmware to work in low power crystal mode, everything started up fine. The bootloader started up and then the firmware.


2 - After I reconfigured my firmware for high gain crystal mode, the bootloader started (or at least I think it started). Then the firmware never ran (current draw dropped 8mA). I then used J-Link commander but it reported that JTAG Debug power domain was off


3 - After I reconfigured my firmware to high gain crystal mode, bootloader and firmware started ok.


So it is obvious that I have things working. My question is this


Why did going from low power to high gain crystal mode make the K21 hang? I couldn't really work it out from the clocking block diagram.


Much appreciated if somebody sheds some light on this. It has been bugging me for days.


Many thanks,