Hallo Erik,

I knew THAT you would reply to this post, and WHAT you would reply... {grin}

I must confess, that you were absolutely right, when assuming, that Fahmy could do something wrong with reset circuitry...

Fahmy, your simple RC reset circuitry shows many pitfalls! It does NOT provide any reliable brown-out detection!!! If your supply voltage isn't absolute proper you will have massive problems and we will you see again here with a post like 'Who has experience with multi micro communication, some very strange is happening...'

And if you additional have some EEPROM or flashrom on board, I guarantee you heaviest problems!

RC reset circuit will only work for fast Vcc rise, like it's observed with proper powering up conditions. If Vcc rises slowly for any reason, reset is removed again from micro, BEFORE Vcc has reached nominal level, or even NO reset signal is produced.
And when Vcc falls for any reason, RC reset circuit does NOT reset microcontroller either. So, if undervoltage takes place for any reason, micro is not protected from running ill!!!

If your project is meant seriously, you shouldn't use simple RC reset circuit. Choose a good reset controller with brown-out detection.


Good luck,
Kai