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A+ Core Hardware Tutorial

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Connectors and Cables -ii

USB stands for Universal Serial Bus. The most important features of USB bus include the following:

Plug'n'Play: USB is a truly plug-n-play port. The port is automatically detected by the system, and its ready to use.
Hot plug and unplug: It is possible to insert an USB device and and unplug without affecting the functioning of a computer. You dont need to power-off the computer to remove or insert a USB device.
127 physical devices: A USB can support up to 127 devices. This is much more than what is normally required.
Low cost cables and connectors

USB connectros can be broadly divided into USB A, and USB B. The difference between the two is in the physical layout of pins in the connector. Both are shown in the figure below.

Pin #	Function
Pin 1	+5V DC
Pin 2	Data-
Pin 3	Data+
Pin 4	Ground

USB"A" plugs are used towards the host system and USB "B" plugs are used towards the USB device.

FireWire/IEEE1394

FireWire/IEEE1394 port provides data rates up to 400 Mb/sec. The standard is most suitable for transferring high volumes of information including video, and voice data.

Given below are some of the important features of IEEE 1394 standard:

Based on open licensing system.
Digital transmission with data rates of 100, 200, or 400 mega bits per second (Mb/sec).
Plug and play: Automatically detected by the operating system during start-up or during usage.
Hot pluggable: Cables can be connected and disconnected without turning off power to the computer.
Flexible: You can connect FireWire cables in a daisy-chain or in branching cable configurations.
Peer-to-peer functionality
Compatibility, lower speed USB devices can be connected with higher speed devices.
Supports both asynchronous (Based on request-and-acknowledge form of computer communication, used typically with dial-up modems). and isochronous data transfer.( Continuous, guaranteed data transmission at a pre-determined speed. Useful for video and audio).

4 PIN IEEE1394 (without Power)

A IEEE 1394 Connector schematic

Pin	Function
Pin #1	Twisted-pair B, differential signals, TPB-
Pin #2	Twisted-pair B, differential signals, TPB+
Pin #3	Twisted-pair A, differential signals, TPA-
Pin #4	Twisted-pair A, differential signals, TPA+

6 PIN IEEE1394 (with Power):

IEEE1394 6-pin connector schematic.

Pin #	Function
1	Power, 18-28v no load.
2	Ground
3	Twisted-pair B, differential signals, TPB-
4	Twisted-pair B, differential signals, TPB+
5	Twisted-pair A, differential signals, TPA-
6	Twisted-pair A, differential signals, TPA+

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