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

[kevin_ledinh]

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

Observation:

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,

[Hui_Ma]

Hi,

There with the external crystal circuit design difference for oscillator low-power mode vs. high-gain mode.

In general, the external oscillator circuit will decide which mode using:

Could you provide the external clock circuit schematics?

Thank you for the attention.

Have a great day,
Ma Hui

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