MKL27z turns back to bootloader mode after 15 seconds

[kicad1978]

Hi! I've got a custom circuit with a MKL27z and it worked pretty well, until recently: it stays in application mode for pretty exactly 15 seconds (without beeing responsive) and then automatically turns back to bootloader mode. What could be the reason for this? My FOPT BYTE is 0x3D

[kicad1978]

Hi Kerry! You are right, I forgot to add pullups for NMI_b. However, it should work even without it, since the circuit worked some days ago! Meanwhile, I didn't alter more than soldering some switches on the PCB, which shouldn't have affected the behaviour of the circuit. Neither did I alter the firmware. So, I'm abit baffled about the described behaviour, ie. the MCU changing back to bootloader mode after being pretty exactly 15 seconds in application mode.

[kerryzhou]

Hi kicad1978,

   Sorry for my later reply.

   Yes, I know you don't want to modify the hardware and the software.

   But in the design phase, we need to find the root problem.

   Now, two ways to test it:

1. Find a official board, take an example, FRDM-KL27, you can download your code to the FRDM board, then check, whether it will also turn back to bootloader mode.

   If the FRDM-kl27 also have the problem, we should check the software.

 2. Try to add the external 4.7K to 10k external pull up resistor on your own designed board.

    Then check whether it have the problem.

   Actually, if you check our kinetis L Peripheral Module Quick Reference.pdf, page 23, you can find this description:

  So, you can try it on your side at first.

Any updated information, just kindly let me know!

Have a great day,
Kerry

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[kerryzhou]

Hi Kicad1978,

   Please check your customer board, did you add external 4.7K to 10K pull up resistor in the NMI pin?

   This is very important!

Have a great day,
Kerry

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------