USB – How it Works
The easiest way to connect computer peripherals is through a Universal Serial Bus. The USB is a plug-and-play interface between the PC and the peripherals.
The main advantage of USB is that the device can be plugged in or plugged out without the need of restarting the PC
USB is the short form of Universal Serial Bus, a standard port that helps to connect computer peripherals like scanner, printer, digital camera, flash drive and more to the Computer. The USB standard supports the data transfer at the rate of 12 Mbps.
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USB Specification
Two important aspects are its support capability and total bandwidth. It is capable of supporting 127 devices and has a total bandwidth of 12 Mbit per second which is equal to 1.5 MB per second. Working of a 12 Mbit (full speed device) or a 1.5 Mbit (low speed devices) depends on the total bandwidth of the USB.
USB 2.0 has a maximum signaling rate of 480 Mbit/s and USB 3.0 has a usable data rate of up to 4 Gbit/s (500 MB/s). Who knows what the future reserves?
USB Connections
Each USB device uses the standard A type connector to the USB host or Hub through A type receptacle. The other end of the cable has series B connector which is used to plug into the B type receptacle.
A connector is used for the upstream connection towards the host and B connector for the downward stream to the USB device. When the device is connected to the PC, it activates the host to recognize it. The PC detects the device and manages a control flow between the device and computer.
PC also manages the data transfer between the device and PC. Once detected, the PC sends data to the USB system software to recognize it which then identify the device and assign an address. This address is used to detect the particular USB device. The software controls the input and output data between the PC and device. If the software fails to assign the address, PC will not detect the device.
USB A, B 2.0 and 3.0 Cable Pinout
The USB cable provides four pathways- two power conductors and two twisted signal conductors. The USB device that uses full speed bandwidth devices must have a twisted pair D+ and D- conductors. The data is transferred through the D+ and D- connectors while Vbus and Gnd connectors provide power to the USB device.
usb A&B male & female pinout
usb 3 female pinout
The USB cable has typically four wires to connect the A type connector
USB Hub
The USB Hub is used to connect many devices to the PC using a single USB connector. The hub can detect the attachment or detachment of devices in each port of the Hub. It also distributes power to all the devices connected to it and also detects low speed and full speed devices.
It has two components – A Hub controller and a Hub repeater. The controller enables the Hub to communicate with the PC for configuration and control of devices attached to it. The repeater has hardware support for reset, suspend and resume signals.
I recommend you to use a hub with an external power supply if you want to connect more than 2 or 3 devices because they will absorb a large amount of current and the USB port cannot provide it by itself.
USB Flash Drive
The most commonly used USB device is the Flash drive the commonly called Pen drive. It is a mass storage device capable of functioning like a hard disk of computer.
article updated and edited by P. Marian on Oct 15, 2014
