[and I apologize for sending this out without a tag the first time].

=20

I am looking at a low-power application using a PIC12F683 running under the
low-frequency internal oscillator (31KHz).=20

=20

The reason for the 683 specifically is that it is an 8-pin device with low
power features that I have a few of in stock. All I really need is an 8 or
10 bit ADC and one other I/O pin.

=20

Relatively low power is important as this will run continuously from batter=
y
power. I would like to keep total draw well under 1ma. Running the 683 at
Fosc=3D31KHz should fit well into my power budget without having to get int=
o
sleep and wake-up algorithms. The chip current is rated at less than 100uA
at that speed.

=20

All I really need to do is monitor the battery voltage and switch the gate
on an external FET to run another higher powered device when it is
appropriate to do so based on whether the battery is currently charging or
has recently been charged. For that I need to do an ADC reading once a
second or so and then decide to allow the other device to run for the next
few minutes or so.

=20

Running on a 31KHz clock is far more CPU speed than I think I need for this=
..
Timing is not critical either. A slow clock will also make it much easier t=
o
count off 30 minutes of real time for controlling the external device.

=20

My question is: Can I run the ADC on the 683 with the TAD set to Fosc/2 wit=
h
Tosc driven by the LFINTOSC at 31HKz? All the documentation is clear that
you can't run the ADC clock too fast. Any references to using a slower spee=
d
just seem to recommend that a faster clock would do faster conversions.
Conversion speed is not important to me.=20

=20

I calculate 11 TAD cycles based on Fosc/2 =3D 15Khz to be 700us, which is
still far faster than I require. The question is will the conversion work a=
t
that slow speed?

=20

My sampling circuit will be a relatively high impedance voltage divider off
of the 12V battery, but I'm assuming that if I give the ADC lots of time to
settle (i.e. a large fraction of a second), I should be OK with a 200K+
input impedance.

=20

Thanks

--=20
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