Intel IXP45X, IXP46X manual USB Host/Device Signal Recommendations

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

3.8.1Signal Interface

Table 15.		USB Host/Device Signal Recommendations
			Input/	Pull
	Name			Up/	Recommendations
			Output
				Down
					Positive signal of the differential USB receiver/driver for the USB device interface.
USB_DPOS			I/O	Yes	Use an 18Ω series termination resistor at the source.
					When this interface/signal is enabled and is not being used in a system design, the
					interface/signal should be pulled low with a 10-KΩresistor.
					Negative signal of the differential USB receiver/driver for the USB device interface.
USB_DNEG			I/O	Yes	Use an 18Ω series termination resistor at the source.
					When this interface/signal is enabled and is not being used in a system design, the
					interface/signal should be pulled low with a 10-KΩresistor.
					Positive signal of the differential USB receiver/driver for the USB host interface.
USB_HPOS			I/O	Yes	Use a 20Ω series termination resistor at the source.
					When this interface/signal is enabled and is not being used in a system design, the
					interface/signal should be pulled low with a 10-KΩresistor.
					Negative signal of the differential USB receiver/driver for the USB host interface.
USB_HNEG			I/O	Yes	Use a 20Ω series termination resistor at the source.
					When this interface/signal is enabled and is not being used in a system design, the
					interface/signal should be pulled low with a 10-KΩresistor.
USB_HPEN			O	No	Enable to the external VBUS power source
					External VBUS power.
USB_HPWR			I	Yes	When this interface/signal is enabled and is not being used in a system design, the
					interface/signal should be pulled high with a 10-KΩresistor.
Notes:
1.	Features disabled/enabled by Soft Fuse must be done during the boot-up sequence. A feature cannot be enabled after
	being disabled without asserting a system reset.
2.	Features disabled by a specific part number, do not require pull-ups or pull-downs. Therefore, all pins can be left
	unconnected.
3.	Features enabled by a specific part number — and required to be Soft Fuse-disabled, as stated in Note 1 — only required
	pull-ups or pull-downs in the clock-input signals.

A typical implementation of a USB interface Host down-stream is shown in Figure 11. The Host controller can not be used as a Device controller; however there is a second USB module with a Device controller capability that can be implementation for this application as shown in Figure 12. Note that depending on the data rate required, Low- speed or Full-speed, the 1.5K resistor shown near the device interface must be connected, either on the D+ or D-.

Speed configuration at the Device can be set as stated in note 1 and 2 bellow. For more details, refer to the Universal Serial Bus Specification, Revision 1.1.

Note:

1.If a 1.5-KΩ,pull-up resistor is connected to USB_DPOS line, the USB port is identified as Full-speed (12 Mbps).

2.If a 1.5-KΩ,pull-up resistor is connected to USB_DNEG line, the USB port is identified as Low-speed (1.5 Mbps).

3.The processors’ USB drivers are CMOS. They require series termination resistors on both signals of the differential pair USB_DPOS and USB_DNEG. The value of the series resistor depends upon the variation of the driver’s impedance.

	Intel® IXP45X and Intel® IXP46X Product Line of Network Processors
February 2007	HDD
Document Number: 305261; Revision: 004	39