Hi,
as i said i have tested the WDT by removing the clock source & it reset the MCU until i connect back the clock source
Correct me if I´m wrong .. but as far as I understood you did the "remove clock" with a different software.
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& when i reset it by disconnecting power it works again
I did not mean a pwower cycle. I meant to use the RESET input (pin)
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If you do it in the order you showed us, the WDT_RESET never would happen.
Without the important pieces of code (or maybe all) all we can do is guess.
Guessing is not my way .. thus you need to rely on others.
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I mean there could by many sources
Maybe it´s continously resetting but you don´t see this.
Maybe there is something during start up to prevent (maybe a loop) to prevent proper WDT initialisation.
.. thus my way is to investigate.
But still it´s your choice how to go on.
Klaus
added:
Now you come up with a new idea (before going through the first idea): EMC
For sure EMC is possible. But I never encountered an EMC problem with my circuits. Maybe because I do the PCB layout the correct way, clean power supplies, keeping noise low, keeping traces short ... we don´t know how you did it.
It´s on you whether you show or hide your informations.