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

Hi There,

I am working with a MCU STM32F405VET for any particular purpose. Lets a 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 working externally,https://www.st.com/resource/en/datasheet/stwd100.pdf

If we think as firmware case what it does is watchdog timer system used to 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 swish 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.
I did see in oscillator when I push the switch meaning that 3 and 2 pin of XT1 has been 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.

Why aren't you using the internal WDT?

Mike.

Pommie said:

Why aren't you using the internal WDT?

Mike.

Click to expand...

Do you mean F/W watch dog ? Its running well.
I have updated my firmware.
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 , pull down resistor 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!

Did you answer the question? I don't know. The STM chips have two built in WDTs - are you using them? If not, why?

Mike.

Pommie said:

Did you answer the question? I don't know. The STM chips have two built in WDTs - are you using them? If not, why?

Mike.

Click to expand...

Purpose is updated Firmware works or not or does it fits with H/W.
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 18.
A forward diode can activate them, for toggling crystal switch MCU can go RESET, but its questionable since application display is not clear.

If not, why?

Click to expand...

Dear Sir Mike,

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!

I believe the answer on AAC may be your problem..

I've still no idea if he answered my question or not.

Giving up.

Mike.

Pommie said:

I've still no idea if he answered my question or not.

Giving up.

Mike.

Click to expand...

From what I can gather... The external WD is something like the NMI.. Because "someone" decided that on chip WD's don't work for their application..

BUT!! The external WD isn't resetting the main MCU.. BUT!! the guy on AAC said the RESET pin is much like the pic MCLRE and need to be configured as a reset..

Ian Rogers said:

From what I can gather... The external WD is something like the NMI.. Because "someone" decided that on chip WD's don't work for their application..

BUT!! The external WD isn't resetting the main MCU.. BUT!! the guy on AAC said the RESET pin is much like the pic MCLRE and need to be configured as a reset..

Click to expand...

Dear Sir Rogers,
Perhaps you understand what I wanted to explain.
I did not go through the firmware in detail, WD is independent of MCU timer, so if is not necessary then you can inactivate it.
Last Friday at 2:33 PM post I said I have managed to RESET the system, WD ic works.

Someone said,

Q16 and Q18: It does not have a current limiting resistor. The emitter base current of Q18 is not limited. I am surprised Q18 is not being destroyed. Also need current limiting resistors on Q15 and Q16 .

Click to expand...

KRA10S and KRC105S both has built in bias resistor as written in their datasheet.

MD MUBDIUL HASAN said:

KRA10S and KRC105S both has built in bias resistor as written in their datasheet.

Click to expand...

Bias resistor and current limiting resistor are different kiddies..

Although the KR10 is good ( with heat sink ) for 1.5a Don't assume it stops there.. If they do have in built bias resistors.. all's good
BUT! why so large.... An MPU reset doesn't take much current...

An MPU reset doesn't take much current...

Click to expand...

I do believe so. The pcb was working well.
Driving the system only transistor and base resistor to limit current going from collector to emitter?