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Which Microcontroller To Use For A Frequency Counter

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radiotek

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There are so many different type and families of microcontrollers out there it makes it very difficult to decide which one to buy. There are 8 bit, 16 bit and 32 bit controllers and so many different manufacturers making these chips it really makes it confusing which one to use for your project. I will need a microcontroller that will be able to count frequencies to at least 40 Mhz. Any suggestions or help would be appreciated.
Frank
 

Nigel Goodwin

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There are a number of PIC based 50MHz frequency counters - the first one on a VERY, VERY old Microchip application note, and using 7 segment LED displays - there are later versions though that use an LCD text module instead.
 

ronsimpson

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There are very few micro controllers who's counter will work at 40mhz. As Nigel said, PIC has some parts that work to 50mhz. I have one working.

It is common to have a 'per-scaller' ahead of a slower counter. (divide by 10 or 100)
 

atferrari

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atferrari

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Thanks, in the next days I will make time to read it in detail.
 

Nigel Goodwin

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As Nigel said, PIC has some parts that work to 50mhz. I have one working.
It's hardly 'some' parts - almost all PIC's will work as 50MHz frequency counters, it's nothing to do with the clock speed of the processor, it's using the physical hardware in the chip - which exceeds 50MHz capability.
 

misterT

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It's hardly 'some' parts - almost all PIC's will work as 50MHz frequency counters, it's nothing to do with the clock speed of the processor, it's using the physical hardware in the chip - which exceeds 50MHz capability.
I was wondering about this. AVR datasheet says

"An external clock source applied to the Tn pin can be used as Timer/Counter clock (clkTn). The Tn pin is sampled once every system clock cycle by the pin synchronization logic."

This means that the external clock to Timer/Counter unit (in AVR) must be less than half the system clock. So PICs are better in that respect. What is a typical speed limit for PIC timer/counter (or whatever the peripheral unit is called in PIC)?

EDIT: Apparently most AVRs have also at least one Timer/counter unit that can be clocked asynchronously.
EDIT2: The specs for AVR asynchronous mode says: "The CPU main clock frequency must be more than four times the Oscillator frequency.". So that is even worse than the synchronous mode.. strange. I think the async mode is mainly designed for RTC.
 
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Nigel Goodwin

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This means that the external clock to Timer/Counter unit (in AVR) must be less than half the system clock. So PICs are better in that respect. What is a typical speed limit for PIC timer/counter (or whatever the peripheral unit is called in PIC)?
It's a standard TTL type spec - so 50MHz minimum - it can be used as a counter for an external input independent of the PIC processor, which is just used to read the value out (in a rather clever way, as only half of it can be read directly).
 
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