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I need to measure an external frequency (10..80 kcs)

Question asked by G.Brehm on Sep 18, 2012
Latest reply on Sep 18, 2012 by MikeL

Dear colleagues,

the problem I have is as simple as this:

Between a given interval (e.g. 500 .. 1000mS), I have to measure an

external  frequency in the range of 10..80 kcs. While the WAKE-UP Timer might do the

cyclic wakeup-job and TIMER0 might generate the timeframe for the

incoming freqency (approx. 100ms) , I still need a COUNTER to count

the incoming pulses.

My idea was to use the LFXTAL - input pin for this purpose rather than

reconfiguring the WAKE-UP Timer back and forth every interval.

Is that doable and if yes: what are the constraints of this approach?

 

Or: is there a way to route EXTCLK to the LFXTAL signal path?

(In the preliminary UserGuide on page 9, there is a line shown between  the

functional blocks "LFXTAL" and "EXTCLK" which I can't explain.)

 

BTW: counting external interrupts is a NO-NO, since the system has to run

at the slowest possible FCLK.

 

Does anyone have an idea on how to solve that "problem"?

Thanks in advance,

Georg

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