Mike..
As luck will have it, I am on a project that is almost exactly like yours.
It has a 1.2M crystal, a 32K crystal on the T1 line, a static LCD like you
mentioned, and it runs on 3V.  Our initial prototype with fully functional
software draws the following values.  In fully awake mode, without buzzer or
backlight on, it draws 430uA.  In semi-sleep (T1 wakes every half second,
I'm prestuffing the timer) I measure 89uA.  In full sleep (in which I turn
off the LCD) I measure between 1 and 2 uA.  (Hello?  check that meter
again?)  Keep in mind that every time we turn a peripheral on or off in
sleep, these numbers seem to change somewhat.  Word of caution, there are
conflicting acounts of how to hook up the LCD voltage pins, I tie the top
two together but not to VCC (If you do it works, but drives suddenly to the
mA range), and tie the bottom two together.  Remove the contrast adjustment
for static LCD's.  Compare your datasheet with the PICDEM3 users guide to
get a bigger picture.  Watch all of your externals to ensure that you don't
hog current.  Use external chips that claim super low shutdown current.  And
for God's sake, use low leakage caps in your supply, lest you leak more than
you use.  Electrolytics are not very good.

Chris Eddy
Pioneer Microsystems, Inc.

Mike Harrison wrote:

> Anyone used the 16C924 with a small LCD?
> The data sheet is a bit incomplete in terms of working out the power
> consumption.
> What I want to know is what's the lowest possible power consumption
> in sleep, lcd on, 3.6v, WDT off, INCLUDING the lcd (small, 40x30mm,
> about 30 seg x 2 com).
> I assume the 32K t1 osc is the lowest power, and it can be used to
> wake the CPU every sec. or so. In my app, sleep current dominates -
> avarage current when awake will add about 1uA (awake 1ms per sec at
> 4MHz).
> The data sheet gives values for LCD voltage generation, but NOT the
> LCD module on its own, i.e. with external voltage generation, and
> gives no clue about typical power draw of the LCD itself - obviously
> this is panel dependent, but a rough guide (e.g. power vs. capacitance
> or a couple of specific displays) would have been nice.
>
> Has anyone measured the supply current in a real app ?
> I'd like 15-20uA max - anyone know is this realistic ?
> Any suggestions for other CPUs would be welcome - low cost is very
> important, but OTP preferred to mask.
>      ____                                                           ____
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