Take at look in the Farnell catalog or website. I remember seeing
oscillators that could switch speed. The PIC could switch it`s self then run
a couple of hundred dummy instructions just to make sure everything was
stable then carry on with its business. Alternatively you could have two
oscillator modules and just run them through the appropriate arrangement of
logic to put them under PIC control.

P.S Could you tell me how it goes as I am considering doing this on my
current project using an SX at 50mhz as I only actually need all that speed
at one point in its operation.

Cheers.

Andrew Seddon

> Hi,
>
> I've been looking towards using a PIC for a 'dual speed' operation;
running the
> PIC from a (small) battery during a power failure (sleep then wake up,
even at
> the lower oscillator rate......or maybe run all the time) then resuming
full
> power operation when power is restored. As things go, the oscillator speed
for
> achieving the reduced power mode requirements does not provide enough
processing
> "oomph" when full power is available. Hence, dual-clock operation would be
> beneficial.
>
> I've had a poke around on the mchip site/checked out a few data sheets and
I
> cannot really find too much information or a specific micro that performs
this.
> Mitsubishi etc make micros that specifically support this - is it
blatantly
> obvious how to do this with the PIC and I have missed it, or is it just
not
> possible?
>
> I've seen a posting where an RC oscillator is used where additional
resistance
> is switched in and out via an I/O pin (dual speed) but I don't think RC is
going
> to give me the clock accuracy that is required.
>
> Any comments would be appreciated.
>
> Regards,
>
> Dan
>