Skip to main content
F
freeflyer
Senior II
February 12, 2026
Question

How to interface external watchdog STWD100 with STM32 ?

  • February 12, 2026
  • 2 replies
  • 570 views

I have added an external watchdog STWD100 to an STM32L433, but want to check that I have implemented it correctly.  See schematic below....

 

freeflyer_1-1770899544728.png

 

The STM32 reset pin has a reset button circuit (copied from the Nucleo development board) and an ST Link programming connector (tag connect).

The watchdog needs to work in combination with the reset button and programmer.

The STM32 uses standby and shutdown low power modes, so I cannot use the STM32 internal watchdog as I need to disable the watchdog when in these low power modes.

 

 

 

2 replies

Andrew Neil
Andrew Neil
Super User
February 12, 2026

The datasheet says there's an option of push-pull or open-drain output.

To work with a switch, you'd want open-drain.

 

@freeflyer wrote:

The STM32 uses standby and shutdown low power modes, so I cannot use the STM32 internal watchdog as I need to disable the watchdog when in these low power modes.

The IWDG has a "Low-power freeze" mode for this:

AndrewNeil_0-1770901483718.png

 

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
    F
    freeflyerAuthor
    Senior II
    February 12, 2026

    Thanks

    The watchdog is an open drain output (part number STWD100YNXWY3F)

    The freeze mode only applies to stop and standby, but I use standby and shutdown.  So when in shutdown the watchdog will keep resetting the STM32

     

    Ozone
    Ozone
    Principal
    February 12, 2026

    ... and to add, the manual reset looks a bit overly complicated.

    And I would add a jumper to disable the watchdog - I can tell you from experience you will need it for flashing and debugging.

      F
      freeflyerAuthor
      Senior II
      February 12, 2026

      The manual reset circuit was taken from the Nucleo board schematic...

       

      freeflyer_0-1770904135100.png

       

      Regarding debugging and programming, the watchdog enable is active low and it is pulled up to 3.3V.

       

      So as long as the digital output from the STM32 to the watchdog enable is not pulled low, the watchdog will not be enabled.

       

      Are you saying that during debugging and programming the STM32 digital output (PC8 in this case) will go low and therefore enable the watchdog ?

      Andrew Neil
      Andrew Neil
      Super User
      February 12, 2026

      For Standby, you have IWDG_STBY

      But that's a separate issue - best to start a separate thread for it ...

      A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
      Terms & ConditionsAccessibility statement