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kylepennington
kylepennington
Associate III
December 11, 2016
Solved

Micro only starts with debugger or nRST manually pulled low

  • December 11, 2016
  • 17 replies
  • 3833 views
Posted on December 12, 2016 at 00:44

I am using the STM32F469 on three devices. One device works fine and starts normally after the power is applied. The other two only start operating after the nRST pin is briefing pulled low. There is 3.3V on nRST after powering it up, indicating the power on reset is ok, but the micro fails to start running.

Attaching the STM debugger and checking the MCU core it says it is halted. Clicking run starts the device working.

What could cause the device to power up correctly but not start the program running?

    This topic has been closed for replies.
    Best answer by kylepennington
    Posted on December 14, 2016 at 04:58

    I measured the resistance between the BOOT0 pin and GND and found it was around 40K. There was dodgey connection between the jumper pin and the pull down resistor. Hardwiring the jumper pin to the pulldown resistor fixed the problem.

    Thanks for your suggestions.

    17 replies

    Tesla DeLorean
    Tesla DeLorean
    Guru
    December 12, 2016
    Posted on December 12, 2016 at 02:31

    Anything else driving the pin in your circuit? You don't want any other push-pull drivers on the pin, the pin should have it's own pull-up.

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    kylepennington
    kylepenningtonAuthor
    Associate III
    December 12, 2016
    Posted on December 12, 2016 at 02:55

    No, the pin is currently floating.

    John F.
    John F.
    Associate III
    December 13, 2016
    Posted on December 13, 2016 at 08:58

    Remove 10k pull-up resistor from MCU_RST (pin 31) and add 100n capacitor from pin 31 to Ground (0V digital). Device has internal pull-up.

    kylepennington
    kylepenningtonAuthor
    Associate III
    December 13, 2016
    Posted on December 13, 2016 at 20:11

    Yeah sorry that resistor has already been removed. I tried adding the 100nF cap but it didn't change anything.

    waclawek.jan
    waclawek.jan
    Super User
    December 13, 2016
    Posted on December 13, 2016 at 20:36

    - have you implemented that LED just after reset, BEFORE setting PLL or whatever clock (otherwise we won't believe you it does not start)

    - option bytes are set how?

    - put one scope probe on NRST other on VDD and take the waveform

    - DS states VDD ramp min.20us/V so 2ms/3.3V should be OK

    - pull down BOOT0 harder (don't be shy to ground directly)

    - try shorting FB4

    - I've never seen 2uF2 style of separating decimals (only 2u2 or 2.2uF, or 2M2/2.2M although this is perhaps not used since 80s) - made me think initially what the 2 suffix might meant... :)

    JW

    Tuttle.Darrell
    Tuttle.Darrell
    Associate II
    December 13, 2016
    Posted on December 13, 2016 at 20:47

    I had a board that had a little trouble with power-on reset (STM32F407). I ended up correcting the problem by programming the brownout reset level (level 3 in my case).

    kylepennington
    kylepenningtonAuthor
    Associate III
    December 13, 2016
    Posted on December 13, 2016 at 23:27

    I tried level 3 but it didn't change anything.

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