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What is USB?
Circuit Design Unit
What is USB?
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USB stands for ‘Universal Serial Bus’
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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?
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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?
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For the most part, there are four 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.
What are the types of connectors?
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Next is the miniUSB and then the newest the microUSB. These
types of USB connectors are found on cell phone, cameras,
microprocessing boards (RaspberryPi, Arduino).
How USB Works: an Overview
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USB uses a four or five-wire cable interface.
Two of the wires are used in a differential mode for
both transmitting and receiving data, two wires are
power and ground and the remaining wire is used to
“id” the device.
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 is limited to about 5
meters.
How USB Works: an Overview
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USB has four types of communication transfer modes:
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control,
interrupt,
bulk, and
isochronous.
Control mode
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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, interrupts do not occur in the usual sense. 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.
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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!
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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 “Micro” Pinouts
USB “Mini” Pinouts
USB Voltage
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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.
USB 3.0
WHY USB 3.0?
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USB 3.0, also known as SuperSpeed USB, is the next
evolutionary phase of the Universal Serial Bus, inarguably the
most successful interface standard.
As computer hardware and peripherals continue to expand in
capacity, speed, and portability, the interfaces that connect
them must also advance in these areas.
USB 3.0- A
Certainly the most recognizable form in computing today,
the USB A connector remains largely unchanged from
the 2.0 specification to the SuperSpeed 3.0.
USB 3.0- B
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Unlike the host-connector A
type, the device-end connector
of the USB world receives a
physical upgrade in the 3.0
specification.
The SuperSpeed USB B port is
similar to the square-ish USB B
of the past, but with an
additional level protruding
from the top of the
connector.
This added area contains the
five additional pins used for
SuperSpeed data transfers.
USB 3.0- Micro
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The SuperSpeed standard makes a noble
attempt to provide a new functionality to
USB devices, but will undoubtedly stir up
plenty of confusion with its Micro-A and
Micro-B connectors.
The underlying principle is that some
USB products, including smartphones
and tablets, should be able to function
not only as devices (connecting to a
desktop computer) but also as hosts
(connecting to a printer, keyboard, or
camera).
To do this, a miniature connector set
("Micro") was designed to be crosscompatible with both host ("A") and
device ("B") connectors