[ARM] How to check external watched dog IC when toggling MCU oscillator?

[Hasan2017]

Hi There,


I am working with a MCU STM32F405VET for any particular purpose. Lets say at this time firmware code has burn on MCU. Lets talk about HW issue.

Take a look the datasheet here https://www.qdatasheet.com/datasheet-download/190671/1/ST-Microelectronics/STM32F405VET6
In my design portion a 25MHz oscillator supports MCU for clocking. See the attached file.

In this time a watched dog ic STWD100NXWY3F is working externally,https://www.st.com/resource/en/datasheet/stwd100.pdf


What it does is watchdog timer is as a system monitor to detect and reset an "out of control" microprocessor. When program execution goes awry it will not properly execute the code that restarts the watchdog. In such a case the watchdog timer will timeout and cause a microcontroller reset. In a properly designed system, the reset will correct the error. Is the case of independent watched dog from main MCU timer.

I want to connect a toggle switch in 2 and 3 point of crystal oscillator XT1 and wish to see the input out put of 1 and 4 of U29 watched dog.

No if you look on the circuit diagram, at U29 IC pull up and pull down resistor are visible.
Now according to datasheet of STWD100NXWY3F , EN-PIN should have pull down resistor that should be 62-100k.
What I did is I have change R101 to 51k, then my board does not work.

If I remove it along with R106 then WDO is unstable but after a time MCU is going to RESET!


I did see in when I push the switch meaning that 3 and 2 pin of XT1 has shorted then input of U29 distorted but wont disappeared.

It wont clear instantly , what do you think?


Datasheet of STWD100NXWY3F says, While the system is operating correctly, it periodically toggles the watchdog input, WDI. If the system fails, the watchdog timer is not reset, a system alert is generated and the watchdog output, WDO , is asserted. BUT MY MCU NEVER GOES TO RESET.

Now there is 2 way to reset this MCU.
Inactivated Q15 and Q19 coupled transistor those are use in F/W WD reset. or only drive Q16 and Q18. A forward diode can activate them, for toggling crystal switch, MCU can go RESET, but its questionable since application device display is not clear

 

[KlausST]

Hi,

Confusing.

* The microcontroller already has two watchdog timers inside. Why using an external one?
* We don't see the exact part number of your oscillator
* usually: Never short circuit the output of a crystal oscillator.
If you do: For sure the clock signal is immediately zero (not only distorted as you think) and it may kill the oscillator
* never use a bjt without current limit on base an emitter/collector (Q15 to Q19). It may immediately kill the bjt(s)
* STWD100 output is open_drain. It is made to directly pull down a (weak) *RESET line. No BJTs needed at all.
* You talk about R101, but there is no R101 on your schematic
* we don't see how WD_EN is controlled. From what we see: The WD_EN is pulled_up = watchdog disabled
* you talk about a display. We don't have any informatiin about the type and how it is connected. Also we have no information why it should be cleared on RESET.

Good that you gave links to datasheets. My recommendation: directly link to the manufacturers sources. They are most up to date, most reliable and not full of advertisement. And the manufacturer often also provides additional information like design notes, application notes, example circuits...

From my experience : I used STM32 microcontrollers and others, I very often use watchdog, but never needed an external device. The internal watchdog usually is very reliable and is feature-rich.

Klaus

 

[Hasan2017]

Why using an external one?

Purpose is updated Firmware works or not or does it fits with H/W.

* usually: Never short circuit the output of a crystal oscillator.

Not for a long time, didn't you see on off switch/ interrupt switch?

never use a bjt without current limit on base an emitter/collector (Q15 to Q19). It may immediately kill the bjt(s)

KRA105S and KRC105S are suitable couple. You didn't view full picture, there is nothing can kill E or C.
What level of current do you expect ? does this pair enhance current in output?

No BJTs needed at al

How you will make signaling to MCU?

you talk about a display. We don't have any information about the type and how it is connected. Also we have no information why it should be cleared on RESET.

Previously who handled this project has gone. This is a charger module controller, at display control( display has external pad input) voltage values comes correctly but current does not.
Someone explains just very few information but he doesn't know what to do.

He said, f/w cant make watchdog action in this case. But I do believe WD command has inactivated.
Now looking at left bottom side of circuit you can see 2 signal WADCH_DOG_EVENT and WADCH_DOG_EV_CLEAR is appeared.

What I did is connect a IN4148 at the base of Q15 that goes to pin 1 of U29 WD IC.
Then I stared push and pull the switch again in XT1 and saw the WDO input pulse diminish and MCU got reset.
After "time out" system restart again!