Arduino Forum

Using Arduino => Project Guidance => Topic started by: magnethead794 on Sep 01, 2012, 04:47 am

Title: I2C between 8MHZ & 16 MHz arduinos
Post by: magnethead794 on Sep 01, 2012, 04:47 am
Any issues with doing it? Just wondering. Need to link a FIO and a mega over I2C.
Yes I know level conversion will be needed.

(the other end of the xBee link is a FIO & teensy2.0++ pairing..same deal there)
Title: Re: I2C between 8MHZ & 16 MHz arduinos
Post by: frank26080115 on Sep 01, 2012, 05:29 am
there shouldn't be any issues

level conversion will not be needed, just disable internal pull-up resistors and use external pull-up resistors that "pull" to 3.3V
Title: Re: I2C between 8MHZ & 16 MHz arduinos
Post by: magnethead794 on Sep 01, 2012, 05:43 am

there shouldn't be any issues

level conversion will not be needed, just disable internal pull-up resistors and use external pull-up resistors that "pull" to 3.3V


So the 5V signals coming from the 5V board won't overdrive the 3V3 pins?
Title: Re: I2C between 8MHZ & 16 MHz arduinos
Post by: cmiyc on Sep 01, 2012, 05:46 am

So the 5V signals coming from the 5V board won't overdrive the 3V3 pins?

That's why you use external pull-up resistors.
Title: Re: I2C between 8MHZ & 16 MHz arduinos
Post by: magnethead794 on Sep 01, 2012, 05:51 am


So the 5V signals coming from the 5V board won't overdrive the 3V3 pins?

That's why you use external pull-up resistors.


Doesn't make sense to me, but I'll go with it.
Title: Re: I2C between 8MHZ & 16 MHz arduinos
Post by: cmiyc on Sep 01, 2012, 05:54 am
Research "open collector".

The I2C pins are open-collector.  They need to be pulled-up so if you external resistors and pull them up to 3.3V they become 3.3V pins.
Title: Re: I2C between 8MHZ & 16 MHz arduinos
Post by: magnethead794 on Sep 01, 2012, 05:58 am

Research "open collector".

The I2C pins are open-collector.  They need to be pulled-up so if you external resistors and pull them up to 3.3V they become 3.3V pins.



works for me.