Who knows the history of USB?

(1) fewer interfaces, limiting upgrades (2) resulting in staggered layout of connectors and cables in the chassis (3) troublesome to operate (4) limited speed

In 1994, seven of the world's leading computer and communications companies, including Intel, Compaq, Digital, IBM, Microsoft, NEC, Northern, Telecom and others, established the USB Forum. Telecom and other seven world-renowned computer and communications companies set up the USB Forum. November 1995 formally developed the USB 0.9 Universal Serial Bus (Universal Serial Bus) specification, 1997 began to really meet the USB technology standard peripherals appear. USB 1.1 is the current standard in early 1999, in the Intel Developer Forum conference, the participants introduced the USB 2.0 specification, the specification of the supporters in addition to the original Compaq, Intel, Microsoft and NEC four members, and HP, Lucent and Philips three new members.

2. USB Definition

USB (Universal Serial Bus) Universal Serial Bus, is a technical standard for connecting external serial devices, computer systems connected to peripheral devices (such as keyboards, mice, printers, etc.) input/output interface standards. USB is a specification for the device insertion frame. In the USB mode, all the peripherals are connected outside the chassis, connecting the peripherals do not have to open the chassis; allows peripheral hot plug, without having to turn off the host power. USB uses a "cascade" approach, that is, each USB device with a USB plug to connect to a peripheral USB socket, which itself provides a USB socket for the next USB peripheral connection.

With this daisy-chain-like connection, a USB controller can connect up to 127 peripherals, when in fact there are only 111 peripherals. The distance between each peripheral (cable length) can be up to 5 m. USB can intelligently recognize the insertion or removal of peripherals on the USB chain, and USB provides a good solution for PC peripheral expansion.

3. USB structure and connection

Low-speed, medium-speed, high-speed and other three transmission levels, the USB port is a jack about 7mm * 1mm, there are four signal lines: two lines to provide power, two lines to transmit the information. USB system is mainly composed of the main controller (Host Controller), the USB Hub and the USB peripherals (Peripherals Node). Peripherals Node) comprises the system topology, the main structure of the USB is mostly a tree topology.

Currently there are two common USB connectors, one is "square", the other is "flat", the former is often referred to as the A-type header, the latter for the B-type header. Both connectors have four pins, two in the center to transmit data, two on the side to provide power to the USB device. The connectors are well-designed, so users won't be able to plug them in incorrectly.

The USB cable is divided into two types: high-speed cable and low-speed cable. High-speed cable transmission rate of 12Mbps, mainly used to connect digital cameras, etc. Low-speed cable transmission rate of 1.5Mbps, mainly used to connect the mouse, keyboard, etc.. The cable can provide 5V, 100mA to 500mA DC. USB can theoretically be connected to 127, but the maximum number of connections in the actual test only stays at 111.

The USB specification divides USB into five parts;

(1) Controller: Mainly responsible for executing the commands issued by the controller driver;

(2) controller driver: the controller and the USB device to establish a communication channel;

(3) USB chip driver: to provide support for the USB;

(4) USB devices: including the PC connected to the USB peripheral devices, divided into two categories: a class of devices itself can be reconnected to other USB peripheral devices, the other class of devices itself can not be connected to other peripheral devices; the former is called the set of peripherals; the former is called the set of peripheral devices; the former is called the set of USB peripheral devices; the former is called the set of USB peripheral devices; the former is called the set of USB peripheral devices. peripheral devices; the former is called a hub, the latter is called a device. Or, the hub with other peripherals connected to the USB port, while the device is connected to the computer to complete a specific function and comply with the USB specification of the device unit, such as a mouse, keyboard and so on.

(5) device driver: is used to drive the USB device program, usually provided by the operating system or USB device manufacturers, such as the usual Modem drivers, printer drivers, etc.. In addition, the USB standard also stipulates that all devices must not be connected more than 5 meters, which means that the length of all peripherals to the outside must not exceed 20 meters.

The latest Southbridge chips can only support up to 5 USB ports, so how will the 127 USB peripherals be connected? There is a special USB peripherals - USB hub (UH), which uses different capabilities of the USB management chip, you can then external 1 to 7 USB devices, its role as a power outlet is not enough access to a power strip, equivalent to a relay station, is the realization of the key to multiple USB peripheral connections.

The USB transmission method is divided into four types (for different demands on system resources by devices).

(1)Isochronous transfer mode: This mode is used to connect external devices that require continuous transmission and do not require high data accuracy but are extremely time sensitive, such as microphones, speakers, and telephones. Isochronous transfer mode to a fixed transmission rate, continuous transmission of data between the host and the USB device, in the transmission of data errors, the USB does not deal with these errors, but to continue to transmit new information

(2) interrupt transmission mode: this mode of transmission of data is very small, but the information needs to be processed in a timely manner to achieve real-time results, this mode is mainly used in keyboards, mice, and game consoles and other external devices. This method is mainly used in keyboards, mice, and external devices such as gamepads.

(3) Control transmission mode: This mode is used to handle the data transmission of USB devices from the host computer. It includes device control commands, device status query and confirmation commands. When the USB device receives these data and commands, it will process the arriving data according to the queue based on the first-in-first-out principle.

(4) Batch transfer mode: This mode is used to transfer data that is required to be correct. Printers, scanners and digital cameras are usually connected to the host computer in this way. Among these 4 data transmission methods, except for the isochronous transmission method, the other 3 methods will try to resend the information to ensure its accuracy when an error occurs in the data transmission.

Comparison of USB advantages and disadvantages

USB interface advantages USB interface disadvantages

Comparison of USB advantages and disadvantages Inexpensive Communication between devices is inefficient

Connection is simple and fast, with high compatibility and good scalability

High-speed, the USB2.0 interface has a transmission speed of up to 480Mbps, and the serial port's 4000 times more than the length of the connecting cable is relatively short

USB early unable to popularize the reasons

1. USB peripheral peripherals and the traditional peripheral peripheral peripherals are not significantly different.

2. Interface space was not reserved (occupied by traditional serial communication interfaces and LPT printers), requiring a USB adapter card

3. Insufficient operating system support

4. ATX motherboards were not born

The concept of the USB file is too abstract.

A comprehensive understanding of the USB 2.0 standard

USB 2.0 (Unified Serial Bus) is a computer peripheral connectivity specification jointly developed by a series of leading names in the PC industry, including Compaq, Hewlett-Packard, Intel, Lucent, Microsoft, NEC, and Philips.USB 2.0 adds a high-speed data transfer mode. In addition to the 1.5Mbit/s and 12Mbit/s modes specified in USB 1.1, USB 2.0 adds a "High Speed" mode of 480Mbit/s (60MB/s).

The USB 1.1 specification is now widely used, with speeds (12Mbps) that are about 100 times faster than standard serial ports, support for simultaneous connection of multiple devices, and true "plug-and-play" characteristics. Because of these benefits, USB has been generally favored by peripheral manufacturers. USB specification after more than two years of promotion, and now has been widely adopted by computers, game consoles, audio-visual appliances and other digital products, the new "USB 2.0" specification transfer speeds than the current "USB 1.1" version is even faster than the "USB 1.0" version. "


Onboard Power and Reset buttons are accompanied by an onboard power supply.

To realize USB 2.0, you need to have both hardware and software support. In addition to the Host Controller and other devices installed in the computer and the controller chip built into the hub need to support version 2.0, in addition to the operating system to install the driver software. Controller chips that support USB 2.0 are now being commercialized. Operating systems that support USB 2.0 will also be available at about the same time.

The USB Implementers Forum, a USB standardization group, has released an operational warranty mark for USB 2.0 LSIs, peripherals, and components. The logo can only be used on products that have been tested by a certification body, and USB 2.0 is an interface specification for data transfer speeds of up to 480 Mbit/s.

The USB 2.0 logo is a symbol of the USB 2.0 standard.