Dale,

Turning on the internal pullups should _not_ result in such a jump in
current draw, unless one or more of the pins is connected via a not very
large resistance to ground.

Is one of the other pins, beside the one you are trying to use for wakeup,
pulling a pin down?

Bob Ammerman
RAm Systems

----- Original Message -----
From: "Dale Botkin" <dale@BOTKIN.ORG>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Saturday, March 09, 2002 2:16 PM
Subject: [PIC]: Sleep power & wake-up


> Hi,
>
> I've got a puzzle involving a 12CE674, but applicable to most PICs.  I
> want to put the PIC to sleep drawing as little power as possible, and wake
> up on a pin change.  I can turn on the internal weak pull-ups, enable
> interrupt in pin change, go to sleep, ground a pin, everything works
> great.  Unfortunately, the current draw is about 700uA with my JW test
> mule!  This thing will sit for weeks at a time (maybe longer) on 2 or 3 AA
> bateries, and I don't want it killing the batteries while it's asleep.
> Yes, I have WDT and the ADC off and everything, it's just the weak pullups
> that are sucking electrons, I turn off internal pullups and current drops
> WAY down.
>
> So I figure maybe I can make the pins outputs, drive 'em high and a
> momentary ground will wake them up, since the interrupt on change looks at
> the pin "past" the output drivers -- no joy, of course (yeah, I know it
> was a dumb idea).  The good news is, sleep current is close to zero.  Bad
> news is, grounding the pin causes 23mA current draw but no wakeup.
>
> I'd like to do this without using an external pullup resistor if at all
> possible, but it's not looking too good right now.  Any more ideas?
>
> Dale
> --
> "Curiosity is the very basis of education and if you tell me that
> curiosity killed the cat, I say only the cat died nobly."
>           - Arnold Edinborough
>
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>

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