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Thread: USB not recognised in custom teensy

  1. #1
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    USB not recognised in custom teensy

    Hi all,

    I built a custom teensy and followed the Teensy 3.2 schematic kindly provided by Paul. However, when I plug the USB cable in, I don't see anything come up on my pc. Doing some probing gives the following

    Initially Reset pin is high but when Program is pulled low, Reset is pulled low. Then Reset goes high again when the program button is released.
    When checking the clock signal on PTA0 pin on MK20DX256, I don't see anything. Only when I toggle the program switch do I see the the clock signal. However, my PC still doesn't recognise it.

    I have checked all my connections between the PJRC's pre-programmed MKL02 and MK20DX256. What further debugging could I do?
    Any help is greatly appreciated. Thanks
    Last edited by christeensy; 07-12-2016 at 08:12 AM.

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by christeensy View Post
    What further debugging could I do?
    Maybe build a second board, in hopes the design is ok and the problem is a simple construction error?

    Check everything yet again. Specifically check all the stuff mentioned as prior problems people have encountered. Have someone else not familiar with your design also check it again.

    If all that fails, maybe post diagrams & photos of what you've actually built. If you look at prior custom board threads, sometimes somebody notices the issue - but only when there's actual layout images & photos.

  3. #3
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    Hi Paul, Thanks for your reply. I guess I will check the board design again.
    Do you know what signals I should expect at what pins on the bootloader to ensure the USB is recognized?

  4. #4
    Senior Member PaulStoffregen's Avatar
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    There really aren't any signals you can easily check from the bootloader chip, other than the Program and Reset lines to verify it is alive and responding.

    Look at the many threads listed in the Troubleshooting section of the MKL02 page:

    http://www.pjrc.com/store/ic_mkl02.html

    If your problem turns out to be something not already on that list, I do hope you'll post a followup here when it's resolved.

  5. #5
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    Couple things to check (have stung me before lol)

    Make sure your usb data lines are the correct way round.
    Makes sure you have usb ground connected.
    Make sure PTA4 is NOT grounded! (mk20 will not boot properly!)
    Check the mk20 regulator is outputting 3.3v
    Check for shorts.
    check all grounds are connected.
    What cyrstal did you use? Through hole with caps? or single SMD?

    Regards
    Russell

  6. #6
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    Thanks a lot for your replies. I finally figured out what the problem was. I had a pull-down resistor on one of the Non-maskable Interrupt Pins on the MK20 chip, which meant that the MKL02 could never program the MK20 properly. I guess this is something to look out for in the future. Thanks again for your help.

  7. #7
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    May i ask which pin?

  8. #8
    Senior Member PaulStoffregen's Avatar
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    Must have been Arduino pin 33, which is native pin PTA4, which is pin #26 of the LQPF64 package.

    I'll add this thread to the MKL02 page troubleshooting list. Hopefully that'll help anyone else who might hit this issue.

  9. #9
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    Ah exact same mistake i made then hehe. Spent ages trying to figure out why my board would not boot.

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