On Mon, 9 Jun 2003 22:56:06 +0100, you wrote:

>My previous designs power consumption was not a problem. But I have to =
power
>a circuit based around a 677 PIC chip from a battery (ideally 9 volts) =
and
>power consumption is important. Can anyone give me tips on what kind of
>voltage regulation I should use?
My favorite is the Holtek HT71xx (xx =3D 30, 33 50 for 3,3.3 or 5V). A =
microamp or so quiescent, low
dropout and will take up to 24V in for when mains adapters need to be =
coped with.

>Secondly what methods can I take to reduce the power consumption of the =
PIC
>in sleep mode? Should outputs be set high or low or even set as inputs?
They must be tied somewhere or held to a definite level, close to the =
supply rails - set unconneced
pins as outputs, connected pins in whatever state draws least current.
Care must be taken that inputs can't float or be held at a voltage =
somewhere between the supply
rails, as this will draw a lot of current. =20

=46or low-power apps, the 'finger test' is a useful way of finding =
floating pins. When the unit is in
sleep, watch the power draw as you run your finger round the pins - a =
sidden increase in current
indicates that a pin is unconnected. A more scientific way is to connect =
a 100Hz or so signal
generator (0..5V output if supply is 5V) through a high value resistor =
(e.g. 1M) to each pin in turn
watching for a disproportionate increas in power draw.=20

Remember that RA4 is open-drain, so setting it 'high' will actually make =
it float.=20

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