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Topic: External crystal for Attiny85 (Read 6 times) previous topic - next topic

ProfePaco

Dec 25, 2011, 04:36 pm Last Edit: Dec 25, 2011, 04:39 pm by ProfePaco Reason: 1
I would like to employ an external 20MHz crystal for Attiny85.



I see that the crystal must be attached to pins 2 and 3. And datasheet gives us recommended values for the capacitors. OK.

However, the question is, pins 2 and 3, cannot be used for inputs/outputs if an external crystal is present?

Thanks in advance

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spycatcher2k

Hi - You can use the pins as I/O if you do not use a crystal, You can set the chip to use an internal 8Mhz (or 1Mhz with divide by 8 set). OR run the chip at upto 20Mhz with the crystal & caps.  Having built over 100 projects with 45/85 chips, I have not used a crystal setup yet (other than on my programming board,  just incase I set the fuses to use external clock).
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ProfePaco


Hi - You can use the pins as I/O if you do not use a crystal, You can set the chip to use an internal 8Mhz (or 1Mhz with divide by 8 set). OR run the chip at upto 20Mhz with the crystal & caps.  Having built over 100 projects with 45/85 chips, I have not used a crystal setup yet (other than on my programming board,  just incase I set the fuses to use external clock).


Yes... however in my case I need a lot of power because I have to make 3 FFT from 3 microphones continuously... so 20MHz better than 8. But I do not have pins enough if I use a external crystal.

I need 3 analogs input for the mics and one pin for sending the information to another Arduino.

BenF


... so 20MHz better than 8. But I do not have pins enough if I use a external crystal.

The AtTiny85 has a PLL circuit that can be used as a system clock source for 16MHz (64MHz / 4) operation. All you need is to program the approriate clock select fuse.

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