AVR input capacitance?

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Hi - I'm looking at the datasheet for an AVR (ATTINY45) and it doesn't seem to specify input capacitance. That is... odd.

I'm trying to figure out the maximum number of nodes you can have on an AVR only I2C bus - but that is capacitance limited typically (official spec calls for 400pF max bus capacitance), so it's impossible to tell.

Any ideas?

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From days of yore, I recall 7pf just package capacitance, DIP, one pin to adjacent pins.

The NXP I2C spec talks about a per-node capacitance. I think it says 15pf but might be 10pf. As I recall, this is a MAX device capacitance.

Given a 128 address space (minus a few reserved ones), it says that you can tolerate about 200pf of connection capacitance with a fully loaded system.

Jim

 

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Quote:

Hi - I'm looking at the datasheet for an AVR (ATTINY45) and it doesn't seem to specify input capacitance. That is... odd.

If you look at the datasheet for a "real" AVR (e.g., Mega88/P/PA) :twisted: it does have a note on that in the TWI/I2C section. Max capacitance 10pF which fits in with Jim's 7pF. Also see the note about "not fully tested".

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