Information Technology Reference
In-Depth Information
9
USB and Firewire
9.1 Introduction
The PC is now evolving into a powerful system through:
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Microprocessor developments.
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Improved graphics systems, such as AGP.
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The PCI bus architecture, especially the PCI bridge.
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Improved plug-and-play technology and automated set-up. The USB port aids in its ease
of connection.
USB (Universal Serial Bus) allows for the connection of medium bandwidth peripherals such
as keyboards, mice, tablets, modems, telephones, CD-ROM drives, printers and other low to
moderate speed external peripherals in a tiered-star topology. Its basic specification is:
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Isochronous ('continuous') transfers which supports audio and video. With isochronous
data transfers, devices transmit and receive data in a guaranteed and predictable fash-
ion. USB also supports non-isochronous devices (the highest priority), and both
isochronous and non-isochronous can exist at the same time.
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Standardised industry-wide plug-and-play specification, cables and connections.
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Multiple-tiered hubs with almost unlimited expansion (with up to 127 physical de-
vices), and concurrent operations.
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12 Mbps transfer rate and different packet sizes. It supports many device bandwidth
requirements from a few kbps to 12 Mbps.
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Wide range of device data rates by accommodating packet buffer size and latencies.
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A hot-plug capability which allows peripherals to be connected without powering down
the computer. Dynamically attachable and reconfigurable peripherals.
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Enhanced power management with system hibernation and sleep modes.
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Self-identifying peripherals, automatic mapping of function to driver and configuration.
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Support for compound devices which have multiple functions.
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Flow control for buffer handling built into protocol.
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Error handling/fault recovery mechanism.
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Support for identification of faulty devices.
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Simple protocol to implement and integrate.
