How to define AVR ports (ATtiny84) if using external crystal oscillator

[peter.charles-jones]

I may need to clock my ATtiny84 with an external 8MHz crystal so it’s nice and stable for data reception.

I realise I need to blow fuses to achieve this and that once done, there is no going back (without a VH programmer).

My query is - how do I declare the pins in question? XTAL1 is PB0 and XTAL2 is PB1 - should these be declared as digital input? - do I enable the pull up resistor? Or is one a digital output?

Or should I just not declare them as anything? - this is my hunch as there was talk of amplifiers and the C to ground on each pin don’t seem ‘digital’.

I’ve had a look in the data sheet but could not find what I would call a definitive answer.

I am keen to get this right first time as I only have a few ATtiny84s to play with.

[peter.charles-jones]

I think on reflection that it’s way too late to be setting GPIO pin direction in the setup() code section to make any difference in terms of how to ISP program the chip.

But for my peace of mind, can anyone confirm that I do not need to specify anything about these XTAL1 is PB0 and XTAL2 is PB1 pins?

I think that setting the fuse CKSEL[3:1] as 111 will be sufficient. Please can you confirm this?

[jkwilborn]

From the datasheet…

For a ‘rock’ I think you need to use PB3/PB4…

Sorry can’t post anything else

There may be a better option, might check out this link…

Good luck