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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



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? 


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.