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TM4C1230E6PM: Reset pin keep low level and can't go to debug

Daniel Fang
Genius 11600 points
Part Number: TM4C1230E6PM

Hi

My customer can't debug by Jlink and ICDI after a period of successful use. It report “Cannot find target device”.

Add RC on reset pin, it keep always low level. Measure the resistor between reset and GND, it shows 42Ohm.

Could you let me know why it has 42Ohm impedance and keep low level? What's the internal circuit?  Thanks.

  • 0
    Guru 117855 points

    That 42Ω is spectacularly too low - something is seriously wrong!    Often a 10K resistor - pulling up to 3V3 - is easily able to drive Reset to ~3V3.    Thus - either the MCU has been damaged or some (other) circuit path - between Reset and Gnd. - exists.

    Surely - if customer is a serious one - such test can be repeated upon (another) test board.     And then - it is guaranteed - that NO 42Ω path to Gnd will be noted... (unless that is a "repeated" board lay-out error!)

  • 0 in reply to cb1_mobile
    TI__Guru*** 135355 points
    Hi Daniel,

    I am in agreement with cb1 on this that the 42 Ohm value between reset and ground seems quite far off from expectation. Note that if correctly connected a resistor would be between VCC and Reset, not Reset and GND. This 42Ohm value between Reset and GND is quite a bit troubling

    What RC values were added to the board for the Reset pin? And has it been tried across multiple boards? Was the RC circuit added per Figure 5-2 of the datasheet including recommended range for R and C components? www.ti.com/.../tm4c1230e6pm.pdf

    Is this a fairly new board? How long was 'a period of successful use'? At some point a schematic may be useful for review here, especially if this is a new board/design.
  • 0 in reply to Ralph Jacobi
    Guru 117855 points

    Hi Ralph,

    I read Daniel's post as 420Ω - only noted 42Ω upon your prompting.    That's at least "THREE ORDERS OF MAGNITUDE" OFF - is it not?

    Clearly some "unkind" (likely unadmitted) fate has befallen this MCU.    Both you & I (earlier) asked that, "Tests of additional boards be performed."

    From our (substantial) experience w/ARM MCUs - across multiple vendors - some "horror" MUST have been visited upon client's MCU!    Never/ever has an "Off the Reel" ARM MCU we've deployed (over 7K from you) exhibited such condition!