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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
February 2007 HDD
Document Number: 305261; Revision: 004 37
General Hardware Design Considerations—Intel
®
IXP45X and Intel
®
IXP46X Product Line of
Network Processors
3.7 I
2
C Interface
The IXP45X/IXP46X network processors support I
2
C interface and protocol. The
hardware-embedded block supports transfer rates in Standard-mode at up to 100 Kbps
or Fast-mode at up to 400 Kbps, 7-bit addressing, and Master or Slave mode.
Note: The I2C block does not support 10-bit addressing mode.
Figure 10 shows the schematic for connecting the I
2
C interface to a 256-byte I
2
C
EEPROM, 7-bit addressing mode (Philips* PC8582C-2T/03).
3.7.1 Signal Interface
3.7.2 Device Connection
More information is available from the Intel
®
IXP45X and Intel
®
IXP46X Product Line of
Network Processors Datasheet and the Intel
®
IXP45X and Intel
®
IXP46X Product Line
of Network Processors Developer’s Manual.
Note: Because of the characteristics of the I2C bus (Open Drain/Collector) pull-up resistors
are required. Use 2 KΩ to 10 KΩ. resistors.
The I
2
C-Bus Specification, available from Philips Semiconductors*, states:
The external pull-up resistor connected to the bus lines must be adapted to
accommodate the shorter maximum permissible rise time for the Fast-mode I
2
C-bus.
For bus loads up to 200 pF, the pull-up device for each bus line can be a resistor; for
bus loads between 200 pF and 400 pF, the pull-up device can be a current source
(3 mA max.) or a switched resistor circuit. The actual value of the pull-up is system
dependent and a guide is presented in the I
2
C-Bus Specification on determining the
maximum and minimum resistors to use when the system is intended for standard or
fast-mode I
2
C bus devices.
Table 14. I2C Signal Recommendations
Name
Input
Output
Pull
Up
Down
Recommendations
I2C_SCL I/O Yes
Serial Data.
Use a 4.7-KΩ pull-up resistor.
I2C_SDA I/O Yes
Serial Clock.
Use a 4.7-KΩ pull-up resistor.