Hi. I'm messing around with i2c and attiny, after, some years ago I managed to successfully make a tiny25V talk to a MCP79410 over i2c.
Things changed since my laptop was stolen and I did not have a backup of the libraries I used (nor of the project). Anyhow I tried messing around with it (as you can tell from other topics in this section) and was advised to use the ATTinyCore library, which offer many advantages and so on.
So the problem is this: I wire up the attiny as a slave, making it talk to an arduino nano as master and it works like a treat. Now I want to try and make the attiny as a master, to recreate the old 79410 board. But first I want to try to use it on an empty bus, just to see whether it works. So I left all of the wirings as before (except for the nano who's not there), that means pullups (the following won't work for any value from 1 to 10k) and the connected pin, and I flash the TinyCore master writer sketch on my board.
Guess what: the SDA line works correctly, but the clock is inverted! By inverted I mean that, instead of being normally high and pulled low when needed, it is normally high and gets "released up" when needed.
I tried checking the scope settings (but I really never touched anything) and also switching the probes, to see whether it was a problem specific to one channel or specific to the probes but, whatever setup I use, the SCL line is "normally low".
What do you think am I doing wrong, or what do you think I can possibly investigate?
Please do mind that resetting the tiny as a slave works fine and I can still use it.