Brent Brown wrote:

> > The original question related to an apparent *increase* in current when the
> > WDT was *disabled* (which I don't believe has been explained yet).
> >
> > Bob
>
> Hi Bob,
>
> Yes it was my question. Just to repeat it: PIC16C84 gives an
> apparent increase in current when watchdog disabled. Still haven't
> found an explanation but I'm working on it.


Hi Brent and Bob, I posted a plausible explanation
before. The 16c84 WDT is a "free running RC oscillator"
according to page 47 of its datasheet.

The diagram on the datasheet shows the WDT enable bit
controls the oscillator, but not the multiplexers and
postscaler. Hence these CAN'T be turned off when you
disable the WDT.

Turning off the WDT (AFAIK from the datasheet) simply
stops the RC oscillator, stopping its counter.

Now RC oscillators can be stopped in two states, with
the cap held high, (discharge fet is off) which uses
very little power, or with the cap held low (discharge
fet is on) and this draws full power through the
pull-up R.

Disabling it with the cap held low uses more power than
the running oscillator. It is also the safest way to
leave it, less chance of spurious triggering the input.
I believe that Microchip went for that option in the
16c84, and your current measurements seem to prove it.

I am very keen to see the same test with a 16f84 and
16f84A...
-Roman

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