PLL on crank angle sensor input

[Tom Cloud]

>I thought of using a PLL to phase lock a higher frequency clock to crank, or
>cam sensor to allow more resolution in developing ignition and fuel timing.
>The problem I see is the very large dynamic range required.   We have
>programmable on chip PLLs that would require software intervention to change
>the feedback as the frequency approaches range boundaries.  me

this topic surfaces every-so-often.  I've asked about it and
been told that the PLL circuit is not stable enough.  My experience
with PLL's is limited, but seems t'me that once capture is achieved,
the little guy ought track any rev changes (esp. for stock)
just fine.  Then, there's the total dynamic range, some say
it's too great.  Dunno.  I know that my Ford truck ('82) uses
a four-pointed crank pickup and manages the timing with that.
MSD offers a similar setup now as an aftermarket timing control.
How do they do that without PLL (could use some sort of time
delay from the pulse onset that's modified by rpm so degree
setting is "constant" ... but anything 'derived' is going
to experience some fluctuation).  So, how'd Ford and how
does MSD do it?

Tom Cloud <cloud at peaches.ph.utexas.edu>