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PICList Thread
'Do 12C50Xs have brown out problems?'
1997\09\30@130032 by Steve Lawther

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    A while back, there was a thread on PICs with UARTs etc, getting into
    a lock-up state on brown-out, that a MCLR couldn't clear.
   
    Has anybody had a similar problem on PIC12C508/9s?
    Or would I probably be ok if I use a MAX811 or similar Micro
    supervisor to put the PIC into reset when the supply is below 2.65V.?
   
    (The supply is a big cap that probably won't go to 0 volts in-between
    power-ups)
   
    Thanks in advance,
   
               Steve Lawther
   
    PIC projects etc.:-
   
    http://ourworld.compuserve.com/steve_lawther/ucindex.htm
   
   
   

1997\09\30@175126 by lilel

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Do Popes say Mass?
Do chickens have wings?
Do snakes have teeth?
Do PICS have ports?
Do engineers have bloodshot eyes from staying up too late?
(in other words) yup


>      A while back, there was a thread on PICs with UARTs etc,
>      getting into a lock-up state on brown-out, that a MCLR couldn't
>      clear.
>
>      Has anybody had a similar problem on PIC12C508/9s?

Big time.  ANY micro can be susceptible to brownouts, and if your
product can fail in an unsafe way with a stuck micro, IT WILL.

>      Or would I probably be ok if I use a MAX811 or similar Micro
>      supervisor to put the PIC into reset when the supply is below
>      2.65V.?

Any good design incorporates something like this, especially if it is
mass produced and could fail in an unsafe way.
>
>      (The supply is a big cap that probably won't go to 0 volts
>      in-between power-ups)

Don't count on it.  Power lines have a standard "circuit breaker "
called a recloser.  A recloser will sense an overload, and interrupt
the power for a few milliseconds.  It then reconnects.  If there is
still an overload, it interrupts for a few seconds.  Then if there is
an overload again, it will interrupt power a third time, sometimes
ten seconds.  Can your cap ride through a ten second brownout?  Don't
count on it.
Best Regards,

Lawrence Lile


'Do 12C50Xs have brown out problems?'
1997\10\01@094747 by Martin McCormick
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Lawrence Lile writes:
>ten seconds.  Can your cap ride through a ten second brownout?  Don't
>count on it.

       Even if it could once, can it now?  Electrolytic capacitors are like
old soldiers in that sometimes, they just fade, fade away.

       I think the electrolyte leaks out or dries up and the capacitance
gradually lessens until you notice something wrong.  Cold temperatures
exaggerate the loss of capacitance.

Martin McCormick

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