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Einly
Joined: 10 Sep 2003
Posts: 60
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| Does 16f876 use 40MHz? |
 Posted: Fri Jan 21, 2005 8:30 am |
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Dear all,
I would like to read an input clock frequency up to 36MHz. Does PIC16f876 support that speed? If not, can anyone suggest one chip to me? Thanks
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Einly |
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rwyoung
Joined: 12 Nov 2003
Posts: 563
Location: Lawrence, KS USA
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| Posted: Fri Jan 21, 2005 8:47 am |
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The PIC16F876(A) has a maximum clock speed fo 20MHz (5MIPs).
Look at the PIC18F devices for 40MHz clocks. Remember the clock is divided by 4 internally so a 40MHz PIC is executing 10MIPs.
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Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month! |
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Einly
Joined: 10 Sep 2003
Posts: 60
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| How to read up to 36MHz input signal frequency? |
| Posted: Fri Jan 21, 2005 8:57 am |
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If I would like to read an input signal frequency up to 36MHz, then what type of chip should I use? Is it related to the crystal osc frequency? Can I use PIC16f876 or should I use pic18? Which chip (for 18 series)?
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Einly |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Fri Jan 21, 2005 9:02 am |
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| And do what with the signal? Even a 40MHz PIC isn't going to do anything with it. The internal instruction cycle on a PIC18 @ 40MHz is 10MHz. If you tried to capture a 10MHz signal the timer value would only be 1! |
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rwyoung
Joined: 12 Nov 2003
Posts: 563
Location: Lawrence, KS USA
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| Re: How to read up to 36MHz input signal frequency? |
| Posted: Fri Jan 21, 2005 1:19 pm |
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| Einly wrote: | | If I would like to read an input signal frequency up to 36MHz, then what type of chip should I use? Is it related to the crystal osc frequency? Can I use PIC16f876 or should I use pic18? Which chip (for 18 series)? |
Can you tolerate a divide by 10 (or greater) between your signal source and the counter input on the PIC? If so, add a decade divider to scale back your signal. Or make the divider programmable by the PIC so you can alter the scale to trade resolution vs jitter vs maximum frequency and cover a very large range of input frequencies.
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Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month! |
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