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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262-004US
875
I2C Bus Interface Unit—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
21.0
I
2
C Bus Interface Unit
This chapter describes the I
2
C (Inter-Integrated Circuit) bus interface unit on the
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors, including the
operation modes and setup. Throughout this manual, this peripheral is referred to as
the I
2
C unit.
21.1
Overview
The I
2
C Bus Interface Unit allows the IXP45X/IXP46X network processors to serve as a
master and slave device residing on the I
2
C bus. The I
2
C bus is a serial bus developed
by Phillips Corporation* consisting of a 2-pin interface. SDA (Serial Data/Address) is
the data pin for input and output functions and SCL (Serial Clock Line) is the clock pin
for reference and control of the I
2
C bus.
The I
2
C bus allows the IXP45X/IXP46X network processors to interface to other I
2
C
peripherals and microcontrollers for system management functions. The serial bus
requires a minimum of hardware for an economical system to relay status and
reliability information on the IXP45X/IXP46X network processors to an external device.
The I
2
C Bus Interface Unit is a peripheral device that resides on the internal peripheral
bus (APB) of the IXP45X/IXP46X network processors. Data is transmitted to and
received from the I
2
C bus via a buffered interface. Control and status information is
relayed through a set of memory-mapped registers. Refer to the I
2
C Bus Specification
for complete details on I
2
C bus operation.
21.2
Feature List
The I
2
C is responsible for the following functions:
• Multi-Master capabilities.
• Slave capabilities.
• The I
2
C unit supports both fast-mode operation — at 400 Kbps — and standard
mode — at 100 Kbps. Fast mode logic levels, formats, capacitive loading and
protocols function the same in both modes. For further information, refer to I
2
C
Peripheral for Microcontrollers by the Phillips Semiconductor.
• The I
2
C unit does not support I
2
C 10-bit addressing or CBUS.
21.3
Block Diagram
shows a block diagram of the I
2
C unit.
Fundamentally, the I
2
C bus consists of a single I/O data line (SDA), a single I/O clock,
and synchronization line (SCL). These are the fundamental I
2
C signals. In the I
2
C unit
of the IXP45X/IXP46X network processors, the SDA and SCL lines are controlled by
logic and state machines which use a 33-MHz clock (clk_i2c) that is supplied by the
CRU unit.