What is USB?Circuit Design 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 “hot-

swappable” interface- no more operating system incompatibility, no more restarting before unplugging or plugging in.

What are the types of connectors? 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?

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 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 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, 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. 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 Name Color Notes1 VBUS Red Power2 D- White Data -3 D+ Green Data +4 GND Black Groun

d

USB “B” Pinouts

Pin Name Color Notes1 VBUS Red Power2 D- White Data -3 D+ Green Data +4 GND Black Groun

d

USB “Micro” Pinouts

USB “Mini” Pinouts

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.

USB 3.0WHY USB 3.0?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 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 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 cross-compatible with both host ("A") and device ("B") connectors