Front Panel Solutions; Internal Usb Cables; Conductor Resistance (Table 6-6 From Usb 2.0 Specification) - Intel 855GME Design Manual

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Intel 855GME Chipset and Intel
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Intel 6300ESB Design Guidelines
9.6.6

Front Panel Solutions

9.6.6.1

Internal USB Cables

The front panel internal cable solution must meet all the requirements of Chapter 6 of the Universal
Serial Bus Specification, Revision 2.0 , for High-/Full-speed cabling for each port with the
exceptions described in Cable Option 2. For more information refer to the Intel FPIO design
guideline available at
9.6.6.1.1 Internal Cable Option 1
Use standard High-speed/Full-speed compatible USB cables. These must meet all cabling
requirements called out in Chapter 6 of the Universal Serial Bus Specification, Revision 2.0 .
Recommended motherboard mating connector pin-out is covered in detail in
9.6.6.1.2 Internal Cable Option 2
Use custom cables that meet all of the requirements of Chapter 6 of the Universal Serial Bus
Specification, Revision 2.0 , with the following additions/exceptions.
1. They may share a common jacket, shield and drain wire.
2. Two ports with signal pairs that share a common jacket may combine V
into a single wire provided the following conditions are met:
a. The bypass capacitance required by Section 7.2.4.1 of the Universal Serial Bus Specification,
Revision 2.0 , is physically located near the power and ground pins of the USB connectors.
This is easiest to achieve by mounting the front panel USB connectors and the bypass
capacitance on a small PCB (daughter card). Refer to the front panel daughter card referenced
later for details.
b. Selecting proper wire size: A general rule for replacing two power or ground wires with a
single wire is to choose a wire size from Table 6-6 in Section 6.6.3 of the Universal Serial
Bus Specification, Revision 2.0 , that has ½ the resistance of either of the two wires being
combined. The data is provided for reference in
Table 86.

Conductor Resistance (Table 6-6 from USB 2.0 Specification)

American Wire Gauge
Example: Two 24 gauge (AWG) power or ground wires may be replaced with one 20-gauge wire.
Proper wire gauge selection is important to meet the voltage drop and droop requirements called
out in the Universal Serial Bus Specification, Revision 2.0, at the USB connectors as well as at the
stake pins on the PCB.
216
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6300ESB ICH Embedded Platform Design Guide
http://www.formfactors.org/developer/specs/fpio_design_guideline.pdf
Ohm (
(AWG)
28
26
24
22
20
Table 86.
Ω
) / 100 meters
maximum
23.20
14.60
9.09
5.74
3.58
Section 9.6.6.2.
and ground wires
BUS