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Why is RESET toggling on unprogrammed K22F?

Question asked by Alexander Farley on Oct 24, 2018
Latest reply on Oct 29, 2018 by Alexander Farley

Hi,

 

First off - I'm aware this issue has been discussed all over the place. However, I have not found clear, consistent answers, so I'm asking the question myself to ensure all relevant context is included. 

 

I'm trying to program a blank K22F device on a new PCB design using a PEMicro Multilink Universal. The programmer is indicating that it doesn't see the target. Probing on the SWD lines shows some activity on SWD-IO and SWD-CLK. The RESET line is also toggling in a triangle-waveform around 10us period.

 

So, my questions are:

1) Does the RESET-toggling explain why the Multilink doesn't see the MCU?

2) What is the normal approach for preventing RESET from interfering with programming a blank MCU? Should the pin be pulled down? Pulled up? Controlled by the Multilink?

3) Does Peter Vlna's comment apply to my scenario?

https://community.nxp.com/message/965936?commentID=965936#comment-965936?q=reset%20toggle 

 

I'm not sure if he's saying that reset-toggling indicates a bricked MCU regardless of which particular part we're using, or if that issue is specific to the MPC5746C part.

 

Thanks.

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