USB

USB, short for Universal Serial Bus, is an industry standard developed in the mid-1990s that defines the cables, connectors and communications protocols used in a bus for connection, communication, and power supply between computers and electronic devices. It is currently developed by the USB Implementers Forum.

USB was designed to standardize the connection of computer peripherals (including keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters) to personal computers, both to communicate and to supply electric power. It has become commonplace on other devices, such as smartphones, PDAs and video game consoles. USB has effectively replaced a variety of earlier interfaces, such as serial and parallel ports, as well as separate power chargers for portable devices.

Overview

In general, there are three basic kinds or sizes related to the USB connectors and types of established connection: the older "standard" size, in its USB 1.1, 2.0, and 3.0 variants (for example, on USB flash drives), the "mini" size (primarily for the B connector end, such as on many cameras), and the "micro" size, in its USB 1.1, 2.0, and 3.0 variants (for example, on most modern mobile phones).

USB 3.0

USB 3.0 (renamed to USB 3.1 Gen 1 in 2015) is the third major version of the Universal Serial Bus (USB) standard for interfacing computers and electronic devices. Among other improvements, USB 3.0 adds the new transfer mode SuperSpeed (SS) that can transfer data at up to 5 Gbit/s (625 MB/s), which is about ten times faster than the USB 2.0 standard. USB 3.0 connectors are usually distinguished from their USB 2.0 counterparts by blue color-coding of the receptacles and plugs, and the initials SS.

A successor standard, USB 3.1 (renamed to USB 3.1 Gen 2 in 2015), was released in July 2013 with the new transfer mode SuperSpeed+ that can transfer data at up to 10 Gbit/s (1.25 GB/s, twice the rate of USB 3.0), bringing its theoretical maximum speed on par with the first version of the Thunderbolt interface.

Overview

The USB 3.0 specification is similar to USB 2.0 but with many improvements and an alternative implementation. Earlier USB concepts like endpoints and four transfer types (bulk, control, isochronous and interrupt) are preserved but the protocol and electrical interface are different. The specification defines a physically separate channel to carry USB 3.0 traffic. The changes in this specification make improvements in the following areas:

Adapter

An adapter or adaptor is a device that converts attributes of one electrical device or system to those of an otherwise incompatible device or system. Some modify power or signal attributes, while others merely adapt the physical form of one electrical connector to another.

An electric power adapter may enable connection of a power plug, sometimes called «travel plug», used in one region to a AC power socket used in another, by offering connections for the disparate contact arrangements, while not changing the voltage. An AC adapter, also called a "recharger", is a small power supply that changes household electric current from distribution voltage (in the range 100 to 240 volts AC) to low voltage DC suitable for consumer electronics.

For computers and related items, one kind of serial port adapter enables connections between 25-contact and nine-contact connectors, but does not affect electrical power- and signalling-related attributes.

See also

USB adapter

A USB adapter is a type of protocol converter which is used for converting USB data signals to and from other communications standards. Commonly, USB adaptors are used to convert USB data to standard serial port data and vice versa.

Most commonly the USB data signals are converted to either RS232, RS485, RS422 or TTL serial data. The older serial RS423 protocol is rarely used any more, so USB to RS423 adapters are less common.

Uses

USB to serial RS232 adapters are often used with consumer, commercial and industrial applications and USB to serial RS485/RS422 adapters are usually mainly used only with industrial applications.

Adapters for converting USB to other standard or proprietary protocols also exist; however, these are usually not referred to as a serial adapter.

The primary application scenario is to enable USB based computers to access and communicate with serial devices featuring D-Sub (usually DB9 or DB25) connectors or screw terminals, where security of the data transmission is not generally an issue.