25-08-2017, 09:32 PM
A Technical Introduction to USB 2.0
A Technical Introduction to USB 2.0.pdf (Size: 20.32 KB / Downloads: 77)
USB 2.0 Executive Summary
A core team from Compaq, Hewlett Packard, Intel, Lucent, Microsoft, NEC and
Philips is leading the development of the USB Specification, version 2.0, that will
increase data throughput by a factor of 40. This backwards-compatible
extension of the USB 1.1 specification uses the same cables, connectors and
software interfaces so the user will see no change in the usage model. They will,
however, benefit from an additional range of higher performance peripherals,
such as video-conferencing cameras, next-generation scanners and printers, and
fast storage devices, with the same ease-of-use features as today’s USB
peripherals.
Impact to User
From a user’s perspective, USB 2.0 is just like USB, but with much higher
bandwidth. It will look the same and behave the same, but with a larger choice of
more interesting, higher performance devices available. Also, all of the USB
peripherals the user has already purchased will work in a USB 2.0-capable
system.
Impact to PC Manufacturer
USB 2.0 will provide system manufacturers the ability to connect to high
performance peripherals in the least expensive way. The additional performance
capabilities of USB 2.0 can be added with little impact to overall system cost.
Indeed, high-bandwidth interfaces such as SCSI adapters may no longer be
required in some systems, leading to a net saving of system cost. Simpler
construction will result since only USB connectors will be needed on many future
PCs. Today’s ubiquitous USB connectors will become USB 2.0, superceding
USB 1.1.
Impact to Peripheral Manufacturer
Today’s USB devices will operate with full compatibility in a USB 2.0 system.
The added capabilities of USB 2.0 will expand the market segment for USB
peripherals, while enabling retail products to transition with the installed base.
Support of USB 2.0 is recommended for hubs and higher bandwidth peripherals.
Designing a USB 2.0 peripheral will be a similar engineering effort to that of
designing a USB 1.1 peripheral. Some low-speed peripherals.
What does USB 2.0 add?
USB 2.0 is an evolution of the USB 1.1 specification, providing a higher
performance interface. Today’s USB 1.1 connectors and full-speed cables will
support the higher speeds of USB 2.0 without any changes. Characterization
that has already been done on these cables confirms this compatibility. Analysis
that has been done by the electrical team suggests that a target of 480Mbs is
achievable on USB 2.0. USB 2.0 will specify a microframe, which will be 1/8th of
a 1msec frame. This will allow USB 2.0 devices to have small buffers even at
high data rates.
Support of higher speed USB 2.0 peripherals connected to a hub assumes USB
2.0 hubs as shown in Figure 2. The higher transmission speed is negotiated on a
device-by-device basis and if the higher speed is not supported by a peripheral,
then the link operates at a lower speed of 12Mb/s or 1.5Mb/s as determined by
the peripheral.