MK20DX128VFM5 resetting continuously

[kumarnarendrasi]

Hi,

I am using MK20DX128VFM5 in our design for openSDA programming of K66 based on https://www.nxp.com/downloads/en/schematics/FRDM-K66F-SCH.pdf  design. We have fabricated 5 boards out of that 3 boards got programmed successfully and openSDA is working on these. On rest 2 boards, we are not able to program as K20 is resetting again and again. I had browsed for this problem and found in one post that "maybe mk20 is not programmed and watchdog is enabled which is triggering reset pin to get low again and again". I am using keil uVision and need support to troubleshoot this issue. Can anyone please suggest some solution to this problem.

[Asad_Khan]

Hi Jorge,

One more thing I would like to highlight here, after flashing the bootloader, I checked the reset signal on DSO, it is a square wave of 70kHz with a 10% duty cycle. 

Note: The resistor value is the same as used in the FRMD-K64 board. (4k7 and 10k).

Regards,

M.Asad Khan

[Asad_Khan]

Hi Jorge,

I have designed a custom board using references from the FRDM-64 development board. I copied the complete circuit for the OpenSDA section on my board. Going ahead to work with OpenSDA, I am able to program K20DX128VFM5 MCU for DAP LINK bootloader firmware. Now the issue is, that MCU is not able to detect on Host PC as an MSD after flashing the bootloader firmware. Need your help to resolve the issue. Please suggest if I am doing something wrong.

Regards,

Mohammad Asad Khan

[jorge_a_vazquez]

Hi kumar narendra singh 

Could you share the connections for the Reset pin, did you have a external pull up in this pin? also, what do you have connected to the NMI pin, it could be causing you problems to program, so we recommend an external pull up too.

When a MCU is blank, core is constantly resetting, so it is common to see a sawtooth signal in the reset pin, even with this behavior, you should be able to program the device if the programmer is able to take control of the reset line.

I recommend you to check the following posts:

Reset signal of K64 

Sawtooth on Reset_B K20 

https://community.nxp.com/message/351183 

Hope this helps.

Best regards

Jorge Alcala

[kumarnarendrasi]

Hi Jorge,

Thanks for your valuable support. I didn't had idea about the reset pin behavior before, what you said. I selected JTAG Interface for programming in stead of SWD and also replaced my IC. with SWD interface i was not able to program even the new IC. Later i selected JTAG interface and now i am able to program the new IC.

Regards

Narendra Singh