James,

I use the same method to measure frequency from 40 to 60 with 0.1 Hz
resolution and it works like a dream. Only I use look up table (200
locations) rather than FP math for time to freq conversion.

Regards

Pailoor


James Paul wrote:

>  Pailoor,
>
>  I recently had ocassion to need a frequency measurement too.
>  What I did was to watch the incoming signal for an edge. Which
>  edge you use doesn't matter.  When an edge is found, I clear the
>  RTCC and let it count up.  I then watch for the next similar
>  going edge, and then transfer the count in the RTCC into a
>  holding register.  Then using the floating point math divide
>  routines in the Microchip handbook vol 2, I take the reciprocal
>  of the number in the holding register, an viola', my frequency.
>  I was measuring frequency from about 1Khz to about 5Khz.  The
>  method I used got me to within a few cycles of the actual
>  frequency, which for my application was good enough. You could
>  increase the resolution by using a faster clock if needed.  I
>  don't know how precise you need to be, but this method worked
>  for me. Maybe it will help you directly or at least give you an
>  idea of how to do it.  Sorry, I can't send you the actual source
>  I wrote as it is copyrighted by my employer, but I don't see why
>  you can't use the same idea.  Hope it helps.
>
>                                             Regards,
>
>                                               Jim
>
> On Wed, 24 November 1999, Craig Lee wrote:
>
> >
> > It's not, this is the problem..  Based on the frequency of the
> > input, I then generate the output.
> >
> > > -----Original Message-----
> > > From: pic microcontroller discussion list
> > > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Ravi Pailoor
> > > Sent: November 24, 1999 9:06 PM
> > > To: PICLIST@MITVMA.MIT.EDU
> > > Subject: Re: Needed: freq meas and gen in 12C508
> > >
> > >
> > > If the incoming square wave and the outgoing square wave is the same,
> > > try this.
> > >
> > >         btfss gpio,0    ; bit 0 is input
> > >         bcf gpio,1      ; bit 1 is output
> > >         btfsc gpio,0
> > >         bsf gpio,1
> > >
> > > Regards
> > >
> > > Pailoor
> > >
> > > Craig Lee wrote:
> > > >
> > > > I mostly program in C with the benefit of interrupts,
> > > > but this application calls for small size and price,
> > > > so I thought I'd ask the piclist.
> > > >
> > > > I need to be able to read an incoming square wave, and
> > > > generate an outgoing square wave based on the first.
> > > > The frequency is from 10Hz to 1Khz.
> > > >
> > > > This is probably very easy for the hardcore micro
> > > > guys, I guess I've become a bit lazy with my GUIs and
> > > > high end languages.
> > > >
> > > > I've done it in a 16F84, although a bit glitchy (can't
> > > > trigger well with a scope), but going to the 12C508,
> > > > I'm a bit lost.
> > > >
> > > > Any direction?
> > > >
> > > > Craig
> > >
> > > --
> > > WE DESIGN THE FUTURE
> > > Website : http://www.chiptechnologies.com
> > > Website : http://business.vsnl.com/chiptech
>
> jim@jpes.com