Intel IXP45X, IXP46X 3.0General Hardware Design Considerations, 3.1Soft Fusible Features, Table

General Hardware Design Considerations—Intel®IXP45X and Intel® IXP46X Product Line of Network Processors

3.0General Hardware Design Considerations

	This chapter contains information for implementing and interfacing to major hardware
	blocks of the Intel® IXP45X and Intel® IXP46X Product Line of Network Processors.
	Such blocks include DDR SDRAM, Flash, SRAM, Ethernet PHYs, UART and most other
	peripherals interfaces. Signal definition tables list resistor recommendations for pull-
	ups and pull-downs.
	Features disabled by a specific part number, do not require pull-ups or pull-downs.
	Therefore, all pins can be left unconnected. Features enabled by a specific part number
	and required to be Soft Fuse-disabled, only require pull-ups or pull-downs in the clock-
	input signals. Other conditions may require pull-up or pull-down resistors for
	configuration purposes at power on or reset. Likewise, open-collector outputs must be
	pulled-high.
Warning:	The IXP45X/IXP46X network processors’ I/O pins are 3.3 V only, except for DDR
	SDRAM which is 2.5 V. None of the I/Os are 5-V tolerant.
	Table 2 gives the legend for interpreting the Type field used in this chapter’s signal-
	definition tables.
Table 2.	Signal Type Definitions
	Symbol	Description
	I	Input pin only
	O	Output pin only
	I/O	Pin can be either an input or output
	OD	Open-drain pin
	TRI	Tri-State pin
	PWR	Power pin
	GND	Ground pin

3.1Soft Fusible Features

Soft Fuse Enable/Disable is a method to enable or disable features in hardware, virtually disconnecting the hardware modules from the processor.

Some of the features offered in the IXP45X/IXP46X product line can be Soft Fuse Enabled/Disabled during boot. It is recommended that if a feature is not used in the design, the feature be Soft disabled. This helps reduce power and maintain the part running at a cooler temperature. When Soft Fuse Disabled, a pull-up resistor must be connected to each clock input pins of the disabled feature interface. All other signals can be left unconnected.

Soft Fuse Enable/Disable can be done by writing to EXP_UNIT_FUSE_RESET register, for more information refer to the Intel® IXP45X and Intel® IXP46X Product Line of Network Processors Developer’s Manual and review the register description.

	Intel® IXP45X and Intel® IXP46X Product Line of Network Processors
February 2007	HDD
Document Number: 305261; Revision: 004	17