Download What is USB

What is USB?
Prototyping Unit
What is USB?

USB stands for ‘Universal Serial Bus’



and is the next step in creating a computer
interface that really works universally.
It boasts cross-platform compatibility for
Macintosh, Linux/UNIX operating systems, and all
versions of Windows since 98SE.
The USB connector ports are available standard on
virtually every computing machine manufactured
in the past decade.
Why use USB?

USB is the first cross-platform “hotswappable” interface- no more
operating system incompatibility, no
more restarting before unplugging or
plugging in.
What are the types of
connectors?


There are two types of connectors on USB cables: a long, flat
rectangle for plugging into computers and hubs called 'USB-A',
and 'USB-B‘, a smaller, square connector for plugging into
devices like external CD and Hard drives, scanners, and printers.
How USB Works: an Overview




USB uses a four-wire cable interface.
Two of the wires are used in a differential mode for
both transmitting and receiving data, and the
remaining two wires are power and ground.
The source of the power to a USB device can come
from the host, a hub, or the device can be "self
powered.“
There are two different connector types on each end
of a USB cable. One of these connectors is for
upstream communications, and the other for
downstream. Each cable length (maximum) is limited
to about 5 meters.
How USB Works: an Overview

USB has four types of communication transfer modes:





control,
interrupt,
bulk, and
isochronous.
Control mode

is initiated by the host. In this mode, every data transfer must send data in both
directions, but only in one direction at a time. The control mode is used mainly for
initialization of devices, but it can also be used to transfer small amounts of data.

In interrupt mode, as in control mode, the host has to initiate the transfer of data.
Interrupt mode works by the host querying devices to see if they need to be serviced.

Bulk mode and isochronous mode complement each other in a sense.


Bulk mode is used when data accuracy is of prime importance, but the rate of data transfer is
not guaranteed. An example of this would be disk drive storage.
Isochronous mode sacrifices data accuracy in favor of guaranteed timing of data delivery. An
example of this would be USB audio speakers.
USB Wiring Warning!




Improperly wiring a USB port can result in permanent
and fatal damage to the computer motherboard, the
USB port and ANY peripheral connected to the
motherboard.
It is imperative that the specific USB pin out
assignment is identified before any attempt is made
to connect the cable to the motherboard.
Simply knowing which pin is #1 is not enough
information to properly wire a USB port.
Trial and error will surely result in the destruction of
the computer motherboard, the computer system
and/or any attached peripheral.
USB “A” Pinouts
Pin
1
2
3
4
Name
VBUS
DD+
GND
Color
Red
White
Green
Black
Notes
Power
Data Data +
Ground
USB “B” Pinouts
Pin
1
2
3
4
Name
VBUS
DD+
GND
Color
Red
White
Green
Black
Notes
Power
Data Data +
Ground
USB Voltage



Supplied voltage by a host computer, or a
powered hub port is between 4.75 and 5.25
Volts of Direct Current (DC).
Maximum voltage drop for bus-powered hubs
is 0.35 V from it's computer host, or hub, to
the hubs output port.
Normal operational voltage for USB circuits is
a minimum of 4.75 Volts DC.