Kirk Humphries

limits of the timer module

Discussion created by Kirk Humphries Employee on Jan 27, 2006

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Posted: Wed Nov 23, 2005  10:25 pm

 

Does someone know the limits to the frequency of the signal that the timer can handle???

 


 

Posted: Thu Nov 24, 2005  8:14 am

 

> Does someone know the limits to the frequency of the signal that the timer

> can handle???

 

The clock provided to the timer module is the bus clock. u have to check the frequency of the bus clk, as it is the limiting parameter to the timer.

 

Suppose ur bus clk is at 6Mhz. So, theorotically, ur timer cannot handle signals higher than 6 Mhz. If u apply a prescalar, then the frequency goes down. Suppose u apply a divide by 2 prescalor, then the timer wont be able to handle signals above 3 Mhz.

 


 

Posted: Fri Nov 25, 2005  3:33 am

 

A thot: Turn your thinking around. If it is the upper limits of frequency that are of interest one can drive the micro's external clock from the unknown, variable freq source and thereby accommodate a freq up to 16 mhz (or is it 25 Mhz on the HCS12?), then use the input capture to get interrupts from a known freq source, thereby enabling a compuation of the unknown freq.

 

For example, on an HC11 I drove the clock from a Rubium osc (10 nhz) and used the gps 1 sec ticks to trigger an input capture and thus make a feedback loop to "discipline" the Rube. Practically no glue hardware required.

 

Regards,

 

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