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Author Topic: what is maximum frequency  (Read 1302 times)
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aamir
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« on: August 28, 2008, 12:21:47 12:21 »

What is maximum INTERRUPT  frequency AVR at 5mZ  CAN HANDLE.Ie what shuold be maximum pulse width that can be handleled by external INT0 pin of avr.
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Codeman
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« Reply #1 on: August 28, 2008, 03:55:45 15:55 »

Well, that depends of a lot of things:

Which frequency you are using to clock the AVR?
What is the language you will use? Assembler ?, C ? Basic?
Who long is the code inside the interrupt?
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hate
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« Reply #2 on: August 28, 2008, 07:41:15 19:41 »

5MHz=200ns instruction cycle on AVR family. If I remember correctly 2 cycles for jumping to the interrupt vector and another 2 cycles for jumping to the interrupt service routine makes 4 cycles. If you won't use any other interrupt and don't have any instructions inside the ISR then complete time for the interrupt to be executed make 6 cycles including the 2 return cycles. This makes an easy calculation of 5/6MHZ for the frequency of a single and empty interrupt. You can calculate what you need by adding the cycles your real ISR will use to that calculation!

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Codeman
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« Reply #3 on: August 28, 2008, 09:37:31 21:37 »

If you google for "AVR frequency counter" you will see some examples. This circuits / software will give you an ideia of what you can get from AVR. Most of the software is written in assembler because of the speed.

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