Working With 3.3V I2C FAQ (Frequently Asked Questions)

Working With 3.3V I2C.

3.3V Signals

The I2C Bus is an open-collector bus. Some place on the bus a pull-up on the clock (SCL) and data (SDA) lines hold the lines high when no device is actively pulling a line low. A pull-up to 3.3V is high enough for 5V devices, like our iPorts, to see the signal as a logical one (1). We have tested iPorts down to about 3.1V, and they seem to work OK. This is also true for our I2C Bus Monitor (#MIIC-101).
 

The only thing you should be careful of is the pull-ups inside the iPorts. These pull-ups are to our internal 5V, so if the iPort pull-up switch on the side of the case is ON, an external circuit will see the 5V. Some 3.3V devices may not tolerate the 5V on a pin, and this could damage the 3.3V device.

 iPort Power:

Our iPort (#MIIC-201), iPort/AI (#MIIC-202), and iPort/AFM (#MIIC-203) are 5V devices. They need about 75ma of regulated 5V power to operate. When attached to a 3.3V system, the iPort power should come from our wall power supply, and the power wire in the I2C Bus cable should NOT be attached to the 3.3V system.

Can't find the answer to your question here? Then e-mail your question to us at support@mcc-us.com