Intel IXP46X Computer Hardware User Manual

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Intel

IXP45X and Intel

IXP46X Product Line of Network Processors

February 2007 HDD

Document Number: 305261; Revision: 004 39

General Hardware Design Considerations—Intel

IXP45X and Intel

IXP46X Product Line of

Network Processors

3.8.1 Signal Interface

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.

Table 15. USB Host/Device Signal Recommendations

Name

Input/

Output

Pull

Up/

Down

Recommendations

USB_DPOS I/O Yes

Positive signal of the differential USB receiver/driver for the USB device interface.

Use an 18Ω series termination resistor at the source.