13.22.6.3.3 4-Wire Mode

Writing a '1' to the Pin Usage bit in the Control A register (CTRLA.PINOUT) will enable 4-wire mode operation. In this mode, the internal I2C tri-state drivers are bypassed, and an external I2C compliant tri-state driver is needed when connecting to an I2C bus.

Figure 13-120. I2C Pad Interface