AVR Reset Problem

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I am using the AT90S2313 in a pulse generating project but I am having
trouble getting the AVR to come out of reset.

When I reset, or initially apply power, the AVR will not proceed to
execute until I ground Pin 4, which is one of the crystal pins.

I am using a 10Mhz crystal, with the standard 22 pF caps to ground.

I was having the same problem when I was using breadboard so
I made a small board for the AVR and soldered the crystal and caps
directly to the avr.

Am I being naive and this is this normal operation?

Could it still be noise?

Sincerely,
James


Re: AVR Reset Problem
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Try to use "supervisor" like MCP100 or something like this.

Maybe you power rising front is't fast.


Re: AVR Reset Problem
A 1k resistor from the reset pin to 5V and a 100n cap to ground should do
the trick...


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Re: AVR Reset Problem
: A 1k resistor from the reset pin to 5V and a 100n cap to ground should do
: the trick...

AVR site docs recommend 4.7K and .01uf (100nf).  I've used that and it
works well.  Using a 10K and .1uf does NOT work well, so the reset line
is a bit tempermental on AVR's I think.

DLC


:> > I am using the AT90S2313 in a pulse generating project but I am having
:> > trouble getting the AVR to come out of reset.
:> >
:> > When I reset, or initially apply power, the AVR will not proceed to
:> > execute until I ground Pin 4, which is one of the crystal pins.
:>
:> Try to use "supervisor" like MCP100 or something like this.
:>
:> Maybe you power rising front is't fast.
:>



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Re: AVR Reset Problem


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I've always used 10k and 100n without any problems.

Leon


Re: AVR Reset Problem
Fri, 21 Nov 2003 10:16:23 +1300, AVRFreak :

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Not if rising front is very long.

Supervisor or WDog is the best choise.
But if you choise a bad soldering flux....

Re: AVR Reset Problem
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Unlike others already pointed out, this has IMO nothing to do with a proper
reset signal. 22p caps are ofter recommended but too low. A crystal is
specified to be loaded with 25pF. The two 22p caps are in series from the
crystals' point of view, thus too low. The capacitance of the AVR is added
to this but is mostly not more that 5 to 10 pF. I always use 33pF at least
(and up to 47p when the crystal frequency should really be spot on). And
another very important thing is proper grounding of the caps. So use a small
groundplane underneath the crystal and caps and connect that plane with the
ground pin of the AVR in the sortest way possible.

Meindert



Re: AVR Reset Problem
...
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...
What means standard in this case?
Are such values for caps specified in the crystal datasheet?
Maybe it is "simple" case when used capacitance did not match crystal
charcteristics and it cannot start oscillating. When you ground pin 4
you also change circuit capacitance for the moment and it causes start
of crystal oscillation.

Regards,
--
Artur Lipowski

Re: AVR Reset Problem

I would agree with the response from Meindert Sprang. The 22pf caps are probably
just
a bit low. I think you'll find that the lower the value of the caps the faster
the
osc will start up and the more likely it will fail to start at all. If you go
with
higher value caps the startup time will be a bit longer, not usually a problem,
but
it will startup reliably. Btw, I've used reset timing as high as 10uf and 10k
with no
problems at all. The only time I've ever had problems with a slow power source
was
with a switchmode supply that had to have soft start and that was fixed using a
power
supervisor circuit.

Mike

On Thu, 20 Nov 2003 12:42:57 -0500, "J. McMillan"

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