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question about PWM

 
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Nick
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question about PWM
PostPosted: Mon Oct 04, 2004 7:29 pm     Reply with quote
"20MHz crystal seems to be 1.22 KHz (per Microchip manual)" via a search.

So I downloaded the datasheet but I didnt see any type of refence chart with that data for 4mhz.

I want to get in the range of 10hz or so.


btw I have a 16f876


Nick
Haplo



Joined: 06 Sep 2003
Posts: 659
Location: Sydney, Australia

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PostPosted: Mon Oct 04, 2004 10:02 pm     Reply with quote
You have to use the formulas in the datasheet to calculate the minimum possible frequency. For a 4MHz crystal it would be about 240Hz.

If you need a 10Hz wave you'll need to implement it using Timer/Compare interrupts.
J_Purbrick



Joined: 16 Sep 2003
Posts: 9

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PostPosted: Tue Oct 05, 2004 11:04 pm     Reply with quote
"20MHz crystal seems to be 1.22 KHz (per Microchip manual)" was a quote from one of my postings! To get a complete sentence, it should have read something like, "The slowest PWM rate you can achieve with a 20MHz crystal seems to be 1.22 KHz (per Microchip manual)".

If you want to use the built-in PWM generator you'd have to run it with a ridiculously slow oscillator to get 10Hz. Better to do it in software.
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