The universal serial bus (USB) is a computer serial bus which enables users to connect peripherals such as the mouse, keyboard, modem, CD-ROM, scanner, and printer, to the outside of a computer without any configuration. Personal computers equipped with USB will allow the user to connect peripherals to the computer, and the computer will automatically be configured as the devices are attached to it. This means that a USB has the capability to detect when a device has been added or removed from a PC. USB is a true plug-and-play bus. Up to 127 peripherals can be connected to a PC with a USB. USB version 1.1 was released in 1998 which supports data rate of 12 Mbps (full speed) and 1.5 Mbps (low speed); the low speed is used for devices such mouse, keyboards, and joysticks. The USB version 2 is a high speed (480 Mbps) that is compatible with USB 1.1 The USB 2.0 specification was developed by seven leading computer manufacturers and it was announced in 1999. The maximum cable length for USB is 5 meters.
USB Architecture:- the USB system is logically a tree topology but physical is a star topology because each USB device communicates directly with the Root Hub. There is only one host Controller in any USB system.
A USB system consists of USB host controller, USB root hub, USB hub, USB cable, USB device, client software, and host controller software.
Host Controller:- The host controller initiates all data transfer, and root hub provides a connection between devices and host controller. The root hub receives transactions generated by the host controller and transmits to the USB devices. The host controller uses polling to detect a new device and is connected to the bus or disconnected from. Also, USB host controller performs the following functions:
(a) Host controller sets up the device for operation (device configuration).
(b) Packet generation.
(c) Serializer/deserializer.
(d) Process request from device and host.
(e) Manage USB protocol.
Host Computer
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