Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 8 of 8

Thread: Teensy 3.6 Reset Pin

Hybrid View

  1. #1

    Teensy 3.6 Reset Pin

    Simple question. Is the reset pin an active low signal?

    Does it behave as a simple reset, meaning rebooting the processor the same as at power on?


    I have an external watchdog & power supervisory chip (ADM8321WAX30) that I plan to use. My project has several high power solenoids that I have to be absolutely sure don't get 'stuck' on or they'd melt/catch fire.

    So, since I need something external to the processor to kill those drivers, I might as well have it reset the processor too.

    If it's just a typical active low reset, I can throw a pullup resistor on the open drain output of the watchdog and connect it up.

    The other question would be, can it be held in reset until the 3.3V comes up? I'd assume yes ... but better to ask! I've read some other threads were some say you can put a cap on reset to ground, which would work if reset has an internal pullup. But then another thread said the Teensy wouldn't boot when they had an external pull up to 3.3V and cap to ground so....

  2. #2
    Senior Member
    Join Date
    Dec 2016
    Location
    Montreal, Canada
    Posts
    3,211
    yes you just need to ground the reset pin to reset teensy or hold it down to hold it reset, but do not hold it down for exactly 15 seconds before releasing, or else the bootloader would reflash teensy with a blank sketch. The issue with most of those boot issues is due to the powersupply, the capacitor method is more like a bandaid fix. Ideally you’d either use a better PSU, or put on a POR (power on reset) chip that would do exactly what you said, hold reset until voltage stabilizes.

  3. #3
    Senior Member+ Theremingenieur's Avatar
    Join Date
    Feb 2014
    Location
    Colmar, France
    Posts
    2,551
    If I remember well, the 15 second thing applies to the program pin, not the reset pin...

  4. #4
    Senior Member
    Join Date
    Dec 2016
    Location
    Montreal, Canada
    Posts
    3,211
    yup, my bad

  5. #5
    Cool, sounds great.

    Thanks!

  6. #6
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    21,319
    Quote Originally Posted by Geomancer View Post
    If it's just a typical active low reset, I can throw a pullup resistor on the open drain output of the watchdog and connect it up.
    Yes, that's exactly how it's meant to be used.

    There's already a weak pullup resistor built inside the chip. It's fine to add another really pullup. Recommend between 2.2K to 10K.

    Also be aware your watchdog chip isn't the only thing that can pull the pin low. The bootloader also pulls the reset low. The reset pin pulls itself low when the chip initiates its own reset (eg, vis the AIRCR register or the internal watchdog).


    The other question would be, can it be held in reset until the 3.3V comes up?
    Yes, you can do this.


    I've read some other threads were some say you can put a cap on reset to ground
    That's correct. Do not use capacitor. Use a chip that only pulls the pin low at startup, and make sure it's open collector/drain, not a push-pull type.

    A capacitor will play havoc when the bootloader chip needs to reboot the main processor. Remember the reset is open collector, so more than 1 source can pull it low. Your external circuit isn't the only actor here.

  7. #7
    Junior Member
    Join Date
    May 2018
    Posts
    5
    Can I use a pin on the Teensy itself, tied to the reset pin with a 10k pullup resistor?

  8. #8
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    21,319
    If you want to cause a reset, just write to SBC_AIRCR. No external wire required.

    https://forum.pjrc.com/threads/29171...ll=1#post77892

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •