what is maximum frequency

[aamir]

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.

[Codeman]

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?

[hate]

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!

Regards...

[Codeman]

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.

Regards