>> In my understanding, BODEN will hold the chip in reset if Vcc is too low.
>> Its thresholds are set unconditionally to be compatible with 5v, so if
you
>> attempt to run at 3.3, BODEN will always hold the chip in reset.
>>
>> It would have been more useful to have a BODEN_3.3 and BODEN_5.0, or
maybe a
>> BODEN with an adjustable threshold, but Microchip did not do it that way.
>>
>> Can someone else back me up on clearing BODEN for 3.3v designs? I may be
out
>> on a limb here.
>><<
>
> You are right.  You can't use the brownout detect feature with "low
voltage"
> designs because it will detect a brown out even though the power supply is
> correct.
>
> However, this guy's problem runs much deeper.  He is using the PIClist as
a
> substitute for reading the manual.  Not knowing about brown out detect is
a
> legitimate problem a newbie might stumble over, but attempting to run a 5V
> chip at 3.5V without ever checking the electrical specs is just plain
stupid
> or lazy.  This is true of ANY chip, even a simple inverter.

I do not agree with your way to evaluate people that ask help.
I have asked help because I'm in trouble. You have partially reason saying
from your poin of wiev this is a stupid problem, but I have been evaluate
the possibility to use the 16F877 at lover voltage. On the manual on page
151, table 15.0 DS30292B and in the following page I have understand that
the PIC should be used at lower voltage, and in particular I use the PIC at
3,9 Volt.

Now the problem of the oscillator seem solved, because with a couple of
spare gate of a 74HC14 I have put the oscillator  to work in good shape, but
I would like understand why with a 4 Mhz clock the PIC refuse to start, also
making action on PCON.0  register as suggested by Brent.

If at the end of this discussion the answer is "PIC CANNOT BE USEDWITH POWER
SOURCE LESS THAN 5 VOLT", for me is important, because I can decide to power
in other way.

Regards

Leo

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