Intel® PXA255 Processor Developer’s Manual 9-1
I2C Bus Interface Unit 9
This chapter describes the Inter-Integrated Circuit (I2C) bus interface unit, including the operation
modes and setup for the PX A255 processor.

9.1 Overview

The I2C bus was created by the Phillips Corporation and is a serial bus with a two-pin interface.
The SDA data pin is used for input and output functions and the SCL clock pin is used to control
and reference the I2C bus. The I2C unit allows the processor to serve as a master and slave device
that resides on the I2C bus.
The I2C unit enables the processor to communicate with I2C peripherals and microcontrollers for
system management functions. The I2C bus requires a minimum amount of hardware to relay status
and reliability information concerning the processor subsystem to an external device.
The I2C unit is a peripheral device that resides on the process or internal bus. Data is transmitted to
and received from the I2C bus via a buffered interface. Control and status information is relayed
through a set of memory-mapped regist ers. Refe r to Th e I 2C -Bus Specif ication for comp lete detai ls
on I2C bus operation.
Note: The I2C unit does not support the hardware general call, 10-bit addressing, or CBUS compatibility.

9.2 Signal Description

The I2C unit signals are SDA and SCL. Table 9-1 describes each signal’s function.

9.3 Functional Description

The I2C bus defines a serial protocol for pa ssing i nf or mation bet ween agen ts on th e I 2C b us us ing a
two pin interface that consist s of a Serial Data/Address (SDA ) line and a Serial Clock Line (S CL).
Each device on the I2C bus is recognized by a unique 7-bit address and can operate as a transmitter
or as a receiver in master or slave mode. Table 9- 2 lists the I2C operation modes.
Table 9-1. I2C Signal Description
Signal Name Input/Output Description
SDA Bidirectional I2C Serial Data/Address signal
SCL Bidirectional I2C Serial Clock Line signal