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MK20DN128VFM5 - SWD Does not connect

Question asked by mjg8t on May 15, 2015
Latest reply on May 20, 2015 by mjg8t

Hi There,


I am now having problmes getting a custom desing to connect with the MK20DN128VFM5.  I finally figured out an unconnecting SWD issue on a previous custom K22F board  that I thought I might be having the same issue on - not the case.  Previously the problem was the NMI triggering interrupts which would not allow SWD connection (k22f - no longer connects to SWD ) - reference: k22f - no longer connects to SWD .


Based upon the reference manual section 6.3.4 the only pins that would conflict with the SWD connection process are the NMI/EZ_PORT_CS(PTA4)  and the reset pins.  However, I have ensured the that PTA4 is held high during the boot process, observed the reset pin coming high after power on and SWD will not connect.


  • I have previously designed a board with a PK20 (pre-qualified 1n86b silicon) chip pcb which have used in the past and based this current design on the working design. 
  • I test the MK20 1n86B silicon chip on the previously running custom board and it will not connect to SWD. 
  • I test the PK20 1n86B on my new board and it connects to SWD no problem
  • I test the MK20 Nn86B on the K22F freedom board (SDA chip location) and it will not connect using SWD.
  • I pull an Mk20 3n86B (latest silicon version) chip off of a K22F freedom board and test it on my current design and it connects no problems!



  1. So it appears that the issue is within the MK20 1n86B silicon version of the chip and I cannot find any reason that SWD would not connect based upon all of the information in the silicon errata.  Any further ideas to what might be causing this silicon version to not properly boot/ connect to SWD?
  2. The easy solution would be to get a hold of the latest silicon version MK20 3n86B chips.  I just ordered some MK20DN128VFM5 from digikey and I recieved the old 1n86B silicon chips.  Is there anyway to order and ensure I receive the latest silicon?