I2C Interface

Bus Protocol

The transfer protocol starts with a start condition followed by a seven-bit or ten-bit device address and a read or write bit. The receiving device must acknowledge each byte by pulling the data line low during the ninth clock pulse. Stop conditions terminate the transmission and release the lines for other devices on the shared bus.

Physical Pullup

Because the bus lines are open-drain, external pullup resistors are required to restore the high logic level. The value of these resistors is selected based on the total bus capacitance and the desired speed. High capacitance slows down the rise time of the signals, which can cause communication errors if the resistor values are too high.

Choosing a smaller resistor increases power consumption during low logic states.

Data Rate

Different operating modes define maximum communication speeds ranging from one hundred kilobits per second to several megabits per second. System designers verify the signal integrity by measuring the rise and fall times under maximum bus loading.