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[on:]

Hi!

I have started a new project including a 1284P with Maniacbugs bootloader.
This is my first time I use the 1284P.
Right now I am soldering all necessary components to my board. I am confused about the I2C pins.
Should I connect my I2C devices to pins "23 PC1 (D 17)" (SDA) and "22 PC0 (D 16)" (SCL)?
Will the wire library work without any modification?
I really want to do all soldering before I burn the bootloader and upload my software (tested on a atmega328p).

I also have a another question: I use both 5v and 3.3v I2C devices.
The pullup resistors (4.7k) for SDA and SCL is connected to 3.3v. I have modified the twi.c file and removed the part including internal pullup resistors.
What could happen if the internal pullup resistors should be activated? Would it damage the connected 3.3v device?


/Olof

[Reply #1 on:]

Should I connect my I2C devices to pins "23 PC1 (D 17)" (SDA) and "22 PC0 (D 16)" (SCL)?
Will the wire library work without any modification?

Yes, this works just fine. I'm using the '1284p in a project and I2C / Wire works fine as-is without any software modifications.

I can't definitely answer your second question. Anecdotally, I have used I2C devices in a mixed 3v3 / 5v project and I tied my pullups to the 3v3 line. The I2C devices functioned just fine. I didn't even realize the Wire library activated internal pullups on the '328. Your mileage may vary, it probably depends on how sensitive the I2C device is.

Cheers!

[Reply #2 on:]

Steph, thanks for your answer!
Now I can continue with my project