Browse Prior Art Database

Internal USB Expansion Cable with Imbeded Logic

IP.com Disclosure Number: IPCOM000013711D
Original Publication Date: 1999-Nov-01
Included in the Prior Art Database: 2003-Jun-18
Document File: 6 page(s) / 206K

Publishing Venue

IBM

Abstract

Disclosed is a device that allows PCB (printed circuit board) designers to generate additional USB ports. The prots are internal to the PC and invisible to the end user. Additionally, with a slight modification to the device, different number of additional ports can be obtained.

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Internal USB Expansion Cable with Imbeded Logic

    Disclosed is a device that allows PCB (printed circuit board) designers to generate additional USB ports. The prots are internal to the PC and invisible to the end user. Additionally, with a slight modification to the device, different number of additional ports can be obtained.

Background

Advantages of USB

The USB was developed with many features in mind. The following presents a list of features that make USB so compelling:

Bandwith - USB has maximnum throughput of 12 Mbps with an option of a low cost 1.5 Mbps interface. In comparison, the common serial port has a bandwidth of 110 Kbps and the parallel port has 2 Mbps. This high bandwidth has two advantages. One is that high bandwidth devices such as cameras can be used. The other advantage is that multiple devices can share this bandwidth and co-exist on the same controller.

Expandable - One USB port can turn into 7 connectable ports by using a hub, which can then be turned into 49. Most of USB hubs only implement a fan-out of 4.

Hot Swappable - Under some operating systems (OS), for example, Micosoft Windows 98, a USB device can be plugged into a USB port at any time and then be instantly recognized and configured by the OS. A USB connected device can also be unplugged at any time with no harm to the system.

Cost - The total cost of adopting USB is relatively low. The actual USB cable has 4 wires with some shielding for the high-speed cable and no shielding for the low speed wire. Although the silicon is more expensive than the traditional serial port, the total additional cost of implementing USB is minimal.

Universal - The technology is general enough that almost all peripherals can be switched to USB, including speakers, microphones, secondary storage devices, and network devices (analog modems, DSL, and Ethernet).

Bus Powered - The bus itself provides up to 500 mA to each peripheral. This means that low power devices do not require a separate power supply.

Problem Analysis

The number of USB devices in the market has been increasing over the last few years. This is coupled with PC manufacturers moving away from legacy support, resulted in an increase of number of USB devices attached to the PC. As the number increases two problems may occure. The first one is the lack of ports, and the second problem is a lack of bandwidth.

Number of ports - It would be very convenient if more than two USB devices could plug directly into the PC. Every PC requires a mouse and a keyboard, which requires 2 USB ports. In the age of internet, a common PC would include additional USB ports for a camera and microphone for video conferencing. Needless to say, two ports would not suffice for this application.

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Bandwidth - In the common setup described above, port throughput is also an issue. Table 1 lists some common devices and their throuputs. The total required throughput for the above example is approximately 7 Mbps from 6 different d...