> >   X / 370 = 4000
> >   X = 4000 * 370 = 1,480,000 = 169540h
> >
> > >From the hex value of X you can see that a minimum of 21 bits are
required
> > for X.  That means you can use a 24 or 32 bit integer divide routine.
>
>
> Thanks again Olin, that all makes perfect sense. Now
> I have the rouble of getting enough resolution at the
> other end of the range. My big period is 10kph=200,000
> so I would be doing:
> (10kph) 1,480,000 / 200,000 = 7.4
> (11kph) 1,480,000 / 182,000 = 8.1
> (12kph) 1,480,000 / 167,000 = 8.9
>
> Obviously with rounding this shoots my resolution
> out the window. I need better than 0.25kph and
> prefer 0.1kph throughout the whole range.

Something seems inconsistant here.  If a period of 370 implies 400Km/H, then
10Km/H would be 14,800, not 200,000.  Your 200,000 figure must be for a
different bike configuration, in which case you would be using a different X
(20,000,000 in that case).  Once X has been chosen for the particular bike
configuration so that you get 4000 for 400Km/H, you end up with a value
that can resolve .1Km/H.

By the way, given your potentially large X values, you need to be doing a
32, not 24 bit, divide.  As you mentioned in your other post, you have
16,000 cycles available, which is way more than enough.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, olin@embedinc.com, http://www.embedinc.com

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