Page 109 - DCAP303_MULTIMEDIA_SYSTEMS

Unit 6: Hardware

sleep states is much faster than switching between enabled and suspended states, which notes
allows devices to sleep while idle.
UsB 3.0
The SuperSpeed USB Logo
• USB 3.0: Released in November 2008.

Specified with a maximum transmission speed of up to 5 Gbit/s (640 MB/s), which is over 10 times
faster than USB2.0 (480 Mbit/s), although this speed is typically only achieved using powerful
professional grade or developmental equipment. The USB 3.0 reduces the time required for data
transmission, reduces power consumption, and is backward compatible with USB 2.0. The USB 3.0
Promoter Group announced on 17 November 2008 that the specification of version 3.0 had been
completed and had made the transition to the USB Implementers Forum (USB-IF), the managing
body of USB specifications. This move effectively opened the specification to hardware developers
for implementation in future products. A new feature is the “SuperSpeed” bus, which provides
a fourth transfer mode at 5.0 Gbit/s. The raw throughput is 4 Gbit/s (using 8b/10b encoding),
and the specification considers it reasonable to achieve around 3.2 Gbit/s (0.4 GB/s or 400 MB/s),
increasing as hardware advances in the future take hold.

Connector properties
The connectors specified by the USB committee were designed to support a number of USB’s
underlying goals, and to reflect lessons learned from the menagerie of connectors which have been
used in the computer industry. The connector mounted on the host or device is called the receptacle,
and the connector attached to the cable is called the plug. In the case of an extension cable, the
connector on one end is a receptacle. The official USB specification documents periodically define
the term male to represent the plug, and female to represent the receptacle (see Figure 6.1).

figure 6.1: standard type: a plug and receptacle

Durability

The standard connectors were designed to be robust. Many previous connector designs were
fragile, specifying embedded component pins or other delicate parts which proved vulnerable
to bending or breakage, even with the application of modest force. The electrical contacts in a
USB connector are protected by an adjacent plastic tongue, and the entire connecting assembly
is usually protected by an enclosing metal sheath.
Compatibility
The USB standard specifies relatively loose tolerances for compliant USB connectors to
minimize physical incompatibilities in connectors from different vendors. To address a
weakness present in some other connector standards, the USB specification also defines limits
to the size of a connecting device in the area around its plug. This was done to prevent a device
from blocking adjacent ports due to the size of the cable strain relief mechanism (usually
moulding integral with the cable outer insulation) at the connector. Two-way communication
is also possible. In USB 3.0, full-duplex communications are done when using SuperSpeed
(USB 3.0) transfer. In previous USB versions (i.e., 1. × or 2.0), all communication is half-duplex
and directionally controlled by the host.

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