At 07:20 AM 7/15/2003 -0500, you wrote:
>OK, I know what it does.  When the voltage gets below a certain point,
>it resets the PIC.  I am trying to figure out how that helps anything.
>So, let's say I have something run by a battery, and the battery voltage
>is starting to drop off.  If I reset the PIC, what does that really
>accomplish?  I would guess that the battery voltage is still going to be
>low.

For it to be useful it should inhibit operation of the micro below a voltage
at which the micro (or other bits) are guaranteed to work properly.

Wouter and Philip have already mentioned the main reasons why you might
want it. In my area of work, it's *essential* in most of the applications.

Think of it from another angle- the PIC is not guaranteed to work properly
below a certain voltage; it can do just about anything, including
(especially) those things you fear the most. Just because sample PIC #1 does
not do it does not mean that sample #18 will not. Just because it doesn't do
it 50 times in a row does not mean it won't on the 51st try.

What applications can this be guaranteed to cause no ill effects whatsoever? T
hose are the ones you *don't* need  BOD.

>Can anyone shed some light on this?  What situations would a brown-out
>circuit be really beneficial?

To add to the list, and to go beyond what evils the PIC itself can get into,
imagine I'm controlling a big fat motor with a power MOSFET. The MOSFET
dissipates 1W max when full on, so I specify a DPAK logic level MOSFET and
give it a decent area of Cu on the board, driving it directly off the PIC
with a couple of resistors.

Without the BOD, as the battery dies the MOSFET starts to drop more
voltage (as Vgs decreases). At some point, it desolders itself and falls
off the board. ;-)  My phone rings, oops, it's the customer; and he's NOT
a happy camper.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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