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ATMEGA48 freezes and needs external reset. WDT doesn't reset the micro

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alexhugo

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Hi,
I am using ATMEGA48. I have following peoblems:
1- Whatever I do, I must have external reset circuit. I set the BODLEVEL fuses to be 4.3 volts hoping that BOD will reset my microcontroller when VCC starts going up but it doesn't work that way. I even programmed the RSTDISBL fuse but that doesn't help either.
2- I don't know why touching the capacitor (or the reset pin itself) that is used for reset, hangs the micro. I am using 10K resistor and 100u cap for reset circuit. Please don't say that I should not touch the reset signal. I know that but this means that's very sensitive to noise. Isn't it?
3- When micro freezes because of the problem in item 2, watchdog timer doesn't reset the chip. Watchdog timer works in other times. For example when I remove the wdr (watch dog reset) command, or I don't call the place that has wdr, I see that my micro gets reset but freezing because of touching the capacitor of the reset circuit is not reset by watch dog timer.

Thanks in advance
Alex
 

Hi,
Why do you have a resistor in the reset circuit as it is? Do you mean resetting by pressing a switch, or there's some circuit that resets the micro. You don't need to do anything, just leave the reset pin floating with no parts connected to it, as there is an internal pull-up at the reset pin.
Try and let us know.

Hope this helps.
Tahmid.
 

alexhugo said:
Hi,
I am using ATMEGA48. I have following peoblems:
1- Whatever I do, I must have external reset circuit. I set the BODLEVEL fuses to be 4.3 volts hoping that BOD will reset my microcontroller when VCC starts going up but it doesn't work that way. I even programmed the RSTDISBL fuse but that doesn't help either.
2- I don't know why touching the capacitor (or the reset pin itself) that is used for reset, hangs the micro. I am using 10K resistor and 100u cap for reset circuit. Please don't say that I should not touch the reset signal. I know that but this means that's very sensitive to noise. Isn't it?
3- When micro freezes because of the problem in item 2, watchdog timer doesn't reset the chip. Watchdog timer works in other times. For example when I remove the wdr (watch dog reset) command, or I don't call the place that has wdr, I see that my micro gets reset but freezing because of touching the capacitor of the reset circuit is not reset by watch dog timer.

Thanks in advance
Alex
Click to expand...

100uF is too much for reset. You can use as low as 1uF.

Touching the capacitor hangs the micro: seems that missing or improper ground loop.
 

Thanks tamilnadu and Tahmid
Well! I know 100uf is too much but 1u doesn't reset the micro.
Tahmid, The problem is that this is the only configuration that reset works.
I have set the registers using codevision compiler.
Do you have any settings or program that might be different setting and doesn't need external reset circuit?
Thanks
Alex
 

Hi Alex,


Went through few Google searches, and landed on your post. So let me share my strange and similar experience, I am facing.
I dont have the reset enabled(havent checked box in CV) just pullep up high internally, but its connected to only the ISP pin and nothing else.


And what more even I have used codevision :sad:
My system(ATMEGA8 ) though is running on adapter(AC 230V to DC 7V), and interfacing LCD and DS1307 also driving relays by ULN2038(Even when ULN is not there it happens)
100nF bypass on all ICs


Problem
>Arbitrary reset
>LCD shows junk data
>Resets back to original display on LCD when RESET pin is touched
>Sometimes it freezes completely at odd interavals, unless I touch reset- it looks dead.

Im just an amature starting off with CV, any help or pointers from anyone will be a learning exprience and a big favour.

Thank you.
 

Hey Alex,

Just came back to post this link for you-
http[:]//www[.]atmel.com/dyn/resources/prod_documents/doc2521.pdf

For me including the cap+resistor(10K+1uF)+diode on reset has helped. No resets on touching now:grin:

Good luck.
 

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