Traditional Culture Encyclopedia - Traditional festivals - What does USB mean?
What does USB mean?
Application of USB
With the rapid development of computer hardware, peripheral devices are increasing day by day. Keyboards, mice, modems, printers and scanners have long been known, and digital cameras and MP3 walkmen have followed. With so many devices, how to access personal computers? USB was born for this purpose. USB is an interface that standardizes and simplifies the connection of computer peripheral devices, and its specifications are formulated by Intel (Intel), NEC, Compaq, DEC, IBM (Business Machines Corporation), Microsoft and Nortel. The transmission rate of USB 1. 1 standard interface is 12Mbps, but a USB device can only get 6Mbps transmission bandwidth at most. So you have to connect an external optical drive, at most a six-speed optical drive, and it can't be higher. However, if you want to play MPEG- 1 VCD movies immediately, you need at least 1.5Mbps transmission bandwidth, which USB can do, but it may be very difficult for USB to play MPEG-2 DVD movies with four times the data. If you add AC-3 audio data, it will be difficult for USB devices to play them immediately. Theoretically, a USB interface can support 127 devices, but at present it can't reach this number. In fact, for a computer, the number of connected peripherals rarely exceeds 10, so this number is enough for us to use. Another significant advantage of USB is that it supports hot plug, which means that you can safely connect or disconnect USB devices when you turn them on, thus realizing real plug and play. However, not all Windows systems support USB. There are many different versions of Windows system at present. Among these versions, only the system above Windows98 has good support for USB, and other Windows versions can't fully support USB. For example, the retail version of Windows95 does not support USB, and only the later version of Windows95 bundled with PC supports USB. At present, although USB devices have been widely used, USB2.0 interface is more common, and its transmission speed is 480Mbps. The demand of users is the driving force to promote the development of science and technology, and manufacturers have also recognized this bottleneck. At this time, Compaq, Hewlett-Packard, Intel, Lucent, Microsoft, NEC and Philips jointly formulated the USB 2.0 interface standard. USB 2.0 improves the data transmission speed between devices to 480Mbps, which is about 40 times faster than USB 1. 1 standard. The biggest advantage of speeding up is that users can use more efficient external devices, and peripherals of various speeds can be connected to USB 2.0 lines without worrying about the bottleneck effect in data transmission. So, if you use a USB 2.0 scanner, it's completely different. It only takes about 0. 1 second to scan a 4M picture, and it passes in a blink of an eye, which greatly improves the efficiency. Moreover, USB2.0 can use cables with the same specifications in the original USB definition, and the connector specifications are exactly the same, which maintains the excellent characteristics of USB 1. 1 on the premise of high speed, and USB 2.0 devices will not conflict with USB 1. X devices are used together. USB2.0 is compatible with USB 1. 1, that is to say, USB 1. 1 devices can be used in common with USB2.0 devices, but at this time, USB2.0 devices can only work at full speed (12Mbit/s). USB2.0 has three working speeds: high speed 480Mbit/s, full speed 12Mbit/s and low speed 1.5 mbit/s, in which full speed and low speed are designed to be compatible with USB 1. 1 and USB 1.0. Therefore, when purchasing USB products, don't just listen to merchants promoting USB2.0, but also find out whether it is a high-speed, full-speed or low-speed device. The USB bus is a one-way bus, and the main controller is on the PC, so USB devices can't actively communicate with the PC. In order to solve the problem of communication between USB devices, related manufacturers have developed USB OTG standard, which allows embedded systems to communicate with each other through USB interface, thus getting rid of PC. The new version of USB2.0 specification was renamed as USB standard, and the original USB 1. 1 was changed to USB 2.0 full speed (full speed version), and the original USB 2.0 was changed to USB 2.0 high speed version. At the same time, a new logo was released. It goes without saying that the high-speed USB 2.0 is definitely faster than the full-speed USB 2.0. The USB port of the computer can provide a maximum current of 500mA.
Edit the basic features of this paragraph.
The hardware structure of 1 Universal serial bus
USB uses four-wire cables, two of which are serial channels to transmit data, and the other two provide power for downstream devices. For high-speed peripherals that need high bandwidth, USB transmits data at full speed of 12Mbps. For low-speed peripherals, USB transmits data at the transmission rate of 1.5Mbps, and the USB bus will automatically and dynamically switch the two transmission modes according to the peripheral conditions. USB is a token-based bus. Similar to token ring network or FDDI token-based bus. The USB host controller broadcasts the token, and the device on the bus detects whether the address in the token is consistent with itself, and responds by receiving or sending data to the host. USB manages USB bus power by supporting suspend/resume operations. USB system adopts cascade star topology structure, which consists of three basic parts: host, hub and functional equipment. Host, also called root, root node or root hub, is installed on the motherboard or as an adapter card on the computer. The host includes a main controller and a root hub, and the root hub controls the data flow and control information on the USB bus. Each USB system can only have one root hub, which is connected to the main controller. Hub is a special component in USB structure. It provides a point named Port, which connects devices to the USB bus, detects devices connected to the bus, provides power management for these devices, and is responsible for bus fault detection and recovery. Hub can provide energy for the bus or itself (power is obtained from the outside). Devices that provide energy by themselves can be plugged into hubs that provide energy by buses, but devices that provide energy by buses cannot be plugged into hubs that provide energy by themselves or support more than 4 downstream ports. For example, when the demand for energy equipment provided by the bus exceeds 100mA, it is impossible to connect with the power hub provided by the bus. Functional devices are connected to the bus through ports. USB can also be used as a Hub.
2.2 software structure. Universal serial bus
There is only one host for each USB, and the host includes the following layers: (1)USB bus interface The USB bus interface handles the interconnection between the electrical layer and the protocol layer. From the interconnection point of view, similar bus interfaces are given by devices and hosts, such as serial interface machine (SIE). The USB bus interface is realized by the main controller. (2)USB system USB system uses the main controller to manage the data transmission between the host and USB devices. Its interface with the main controller depends on the hardware definition of the main controller. At the same time, the USB system is also responsible for managing USB resources, such as bandwidth and bus energy, which makes it possible for customers to access USB. USB system also has three basic components: Host Controller Driver (HCD), which can map different host controller devices into USB system. The interface between HCD and USB is called HCDI, and the specific HCDI is defined by operating systems supporting different host controllers. Universal Host Controller Driver (UHCD) is located at the bottom of the software structure, which is used to manage and control the host controller. UHCD can communicate with USB host controller and control it, which is hidden from other parts of system software. The highest layer in the system software communicates with the main controller through the software interface of UHCD. USB driver (USBD) on top of UHCD driver provides a driver-level interface to meet the requirements of existing device driver design. USBD provides a data transmission architecture in the form of I/O request packet (IRP), which requires data transmission through a specific pipeline. In addition, USBD makes the client appear as an abstraction of the device, which is convenient for abstraction and management. As part of the abstraction, USBD has a default pipeline. Through it, you can access all USB devices for standard USB control. This default pipe describes the logical channel for communication between USBD and USB devices. Host software In some operating systems, USB system software is not provided. These softwares were originally used to provide configuration information and loading structure for device drivers. In these operating systems, the device driver will apply the provided interface instead of directly accessing the USB driver interface (USB driver interface) structure. (3) The USB client software is located at the highest level of the software structure, and is responsible for handling specific USB device drivers. The client layer describes all software portals that directly act on devices. When the system detects the device, these client programs will directly act on the peripheral hardware. This unique feature places the USB system software between the client and its device, which needs to be processed by the client program according to the device image formed by USBD at the client. Each layer of the host has the following functions: detecting connected and removed USB devices. Manage the data flow between the host and USB devices. Connect USB status and activity statistics. Control the electrical interface between the main controller and USB devices, including limited energy supply. HCD provides the abstraction of the main controller and the abstraction of the main controller perspective of data transmitted through USB. USBD provides the abstraction of USB devices and the abstraction of data transmission between USBD clients and USB functions. USB system promotes data transmission between customers and functions, and serves as the control point of standard interface of USB devices. USB system provides buffer management function and allows data transmission to be synchronized with the requirements of customers and functions.
3.USB data stream transmission
The main controller is responsible for data flow transmission between the host and USB devices. These transmitted data are regarded as a continuous bit stream. Each device provides one or more interfaces that can communicate with the client program, and each interface consists of 0 or more pipes, which independently transmits data between the client program and the specific terminal of the device. USBD establishes an interface and pipeline for the actual requirements of host software. When a configuration request is issued, the host controller provides services according to the parameters provided by the host software. USB supports four basic data transmission modes: control transmission, synchronous transmission, interrupt transmission and data block transmission. When each transmission mode is applied to a terminal with the same name, it has different properties. The control transmission type supports the transmission of control, status, configuration and other information between peripherals and hosts, and provides a control channel between peripherals and hosts. Each peripheral supports the control transfer type, so configuration and command/status information can be transferred between the host and the peripheral. Synchronous transmission type supports data transmission between peripheral and host, with periodicity, limited delay and bandwidth and constant data transmission rate. This type does not have error checking, so it cannot guarantee correct data transmission, and supports data transmission between computer-telephone integrated system (CTI) and audio system and host computer. Interrupt transmission supports input devices such as gamepad, mouse and keyboard. The data transmission between these devices and the host is very small and aperiodic, but it is sensitive to the response time and needs immediate response. The batch transfer type supports printers, scanners, digital cameras and other peripheral devices. The amount of data transmitted between these peripherals and the host is very large, and USB can only transmit such data when the bandwidth is satisfied. USB adopts block bandwidth allocation scheme. If the peripheral exceeds the current bandwidth allocation or potential demand, it cannot enter the device. The terminals of synchronous and interrupt transmission types reserve bandwidth to ensure data transmission at a certain rate. Centralized and controlled terminals transmit data according to the available optimal bandwidth.
Edit this paragraph USB vs IEEE 1394.
What are the similarities between 1.USB and IEEE 1394?
Both are universal external device interfaces. Both can transmit large amounts of data quickly. Both can be connected to many different devices. Both support hot dialing. Both can be used without an external power supply.
2. What's the difference between 2.USB and IEEE 1394?
Their transmission rates are different. The highest speed of USB can reach 5Gb/s, but because USB3.0 has not been popularized, the current mainstream USB2.0 is only 480Mb/s, and the speed is unstable; In contrast, the current speed of IEEE 1394 is only 800Mb/s, but it is relatively stable. Therefore, the IEEE 1394 interface is kept in high-speed devices such as digital cameras, but the USB interface is also adopted. The structure of the two is different. When USB is connected, there must be at least one computer and a HUB for interconnection. The whole network can have at most 127 devices. IEEE 1394 does not need a computer to control all devices, nor does it need a hub. IEEE 1394 can connect multiple IEEE 1394 networks with bridges, which means that after 63 IEEE 1394 devices are implemented with IEEE 1394, other IEEE 1394 networks can also be connected with bridges. They are different in intelligence. IEEE 1394 network can automatically reset the network when adding or deleting devices. USB uses HUB to judge the increase or decrease of connected devices. The application degree of the two is different. Now USB has been widely used in all aspects, almost every PC motherboard has a USB interface, and USB2.0 will further expand the application scope of USB. IEEE 1394 is only applied to multimedia aspects such as audio and video.
Extended application and development trend of USB
Front USB interface
The front USB interface is a USB expansion interface located on the front panel of the chassis. At present, there are more and more external devices using USB interface, such as mobile hard disks, flash drives, digital cameras and so on. But every time you use these devices (especially frequently used mobile storage devices), you have to drill into the back of the chassis and use the USB interface on the motherboard, which is obviously inconvenient. The front USB interface provides users with good usability in this respect. At present, the front USB interface has almost become the standard configuration of the chassis, and the chassis without the front USB interface is very rare. The front USB interface can only be used if it is connected to the corresponding front USB pins on the motherboard (generally 8-pin, 9-pin or 10 pin, two USB are paired, and each USB uses 4 pins for signal transmission and power supply). When connecting the front USB interface, be sure to read the relevant contents in the motherboard manual and chassis manual carefully in advance, and never connect incorrectly, otherwise it will damage the USB device or motherboard. In addition, because the output voltage of USB2.0 interface is 5V, the output current is 500mA. When using the front USB interface, we should pay attention to the problem of insufficient power supply of the front USB interface. When using a high-power USB device, use an external power supply or directly use the onboard USB interface of the motherboard on the back of the chassis to prevent the USB device from working normally or being damaged.
USB port hard disk box
At present, the mainstream, its biggest advantage is easy to use, supporting hot plug and plug and play. There are two USB standards: one is USB 1. 1 interface, with a transmission speed of only 12Mbps, and the other is USB2.0 interface with a transmission speed of up to 480Mbps. At present, USB on the motherboard supports USB 1. 1, but USB2.0 can only be supported by newer motherboards. When shopping, choose products according to personal circumstances. Although USB2.0 is backward compatible with USB 1. 1, the mobile hard disk box supporting USB 2.0 interface is more expensive than USB 1. 1.
wireless usb
Jeff Ravencraft, chairman of the USB Developer Forum and technical strategy officer of Intel Corporation, said that wireless USB technology will help users get rid of complicated cable connections when connecting printers, digital cameras, music players and external disk drives with personal computers. The data transmission rate of wireless USB standard is the same as that of wired USB 2.0 standard, which is 480M per second. The difference between the two is that wireless USB requires wireless transceiver devices in personal computers or peripherals, rather than cable connections. On the eve of the Intel Developer Forum, Ravencraft said that external disk drives, digital cameras and printers will be the first to adopt this standard. More and more products will be put on the market in the third quarter of this year. In order to make the wireless USB standard practical, some shortcomings of this technology must be improved. The USB standard organization has published the wireless alliance specification, which ensures that computers and peripherals can only be connected through wireless USB after being certified. Ravencraft added that USB standard has been widely used to connect digital cameras, scanners, mobile phones, PDA, DVD burners and other devices with personal computers. The wireless alliance specification specifies in detail how personal computers and peripherals can be connected through wireless USB, and a computer can connect at most 127 peripherals at the same time. The wireless alliance specification stipulates two ways to establish a connection. The first method is to connect the computer and peripherals with cables, and then establish a wireless connection for later use. The second method is that the peripheral device can provide a series of numbers, which the user can input into the computer when establishing the connection. Wireless USB uses ultra-wideband technology to communicate. At present, the 802. 1 1g protocol of WLAN uses the short frequency band around 2.4GHz for communication, while the ultra-wideband technology uses the frequency band from 3. 1GHz to 10.6GHz for communication. The signal level of UWB is low enough, so the influence of UWB signal is similar to noise for other wireless communication technologies. At present, the technology widely used in wireless networks is IEEE 802. 1 1 standard, which is Wi-Fi promoted by Intel. This technology is widely used in notebook computers, and even some digital cameras of Nikon and Canon have adopted this technology. Wireless USB technology is a completely different technology. Because it is relatively simple to implement and the power consumption is only half of 802. 1 1, many manufacturers prefer to adopt wireless USB technology. Ravencraft said that the key to adopting 802.438+0 1 technology for high-end mobile phones and digital cameras is to solve the battery life problem. Manufacturers find that ultra-wideband technology is the best way to solve this problem. Within 0/0 foot of the computer/kloc-,the transmission rate of the wireless USB device will be maintained at 480M per second. If it is within 30 feet, the transmission rate will drop to 1 100 m per second. However, with the development of technology, the transmission rate of wireless USB will exceed 1G per second or even faster. At present, UWB technology can be used not only for wireless USB connection, but also for Bluetooth and IEEE 1394 firewire connection, and even for short-distance WiNet connection.
Edit the different interfaces and data lines of this USB.
With the popularity of various digital devices, especially MP3 and digital cameras, there are more and more USB devices around us. However, although these devices all use USB interfaces, the data lines of these devices are not exactly the same.
USB interface (12 block) These data lines are the same at the end connected to the PC, but when connecting the device end, different interfaces are usually used for the sake of size. The connectors of most digital products are the same except those connected to PC, and the other end also follows the standard specifications. USB is a unified transmission standard, but there are many kinds of interfaces, the most common one is the flat one used by our computer, called port A, which has four wires in it. According to who is plugged in, it is divided into male interface and female interface. Generally speaking, wires are male and machines are female.
USB A plug port
The picture on the upper right shows the most common USB Class A common Mini B 5Pin interface: the next is the most common interface in digital products. Due to the limited size of digital products, Mini B interface is usually used, but there are many kinds of Mini B interfaces.
Mini B 5Pin
The picture on the right shows the Mini B 5Pin interface schematic diagram.
This kind of interface can be said to be the most common interface at present. Because of its excellent anti-misoperation performance and compact size, it is gaining the favor of more and more manufacturers. Now it is widely used in card readers, MP3 players, digital cameras and mobile hard disks. The picture below shows the Mini B 5Pin interface on Sony F828. At present, there are Sony cameras, video cameras and MP3 players, Olympus cameras and tape recorders, Canon cameras and HP digital cameras. Quite a few devices use this interface. Common Mini B 4Pin interface: In addition to the most common Mini B 5Pin interface we saw earlier, there are many other Mini B interfaces, some of which are common.
Mini B 4Pin
On the right is the interface of Mini B 4Pin. The picture below shows the patch cord of Mini B 4Pin. This interface is common in digital products of the following brands: Olympus C series and E series, most of Kodak's digital cameras, Samsung's MP3 products (such as Yepp), Sony's DSC series, Compaq's IPAQ series ... Fuji Mini B 4Pin flat interface: Mini B 4Pin flat. There is also a form, that is, Mini B 4Pin Flat. As the name implies, this interface is flatter than Mini B 4Pin, and it is also widely used in devices.
Fuji mini B 4Pin tablet
On the right: Mini B 4Pin flat interface. This interface is very similar to the aforementioned MiniB 4pin, but this connector is flatter and takes up less space. This interface is common in the following devices: Fuji's FinePix series, Casio's QV series cameras, and Konica's products. We can see that Fuji machines use this interface more, and almost all the old models use this interface. However, it is worth noting that Fuji has given up this interface on the latest S5000 and S7000 and switched to the Mini B 5Pin camp. Nikon's unique mini-B 8-pin interface: In addition to the previous 4-pin and 5-pin mini-B, there is also an 8-pin mini-B interface, which rarely appears on other devices and generally appears on digital cameras. There are also three kinds of mini-B interfaces, one is common, the other is round, and the other is plane interface with 2×4 layout.
Mini b8 pin
The picture on the right shows the Mini B 8Pin interface, which is suitable for this equipment. As far as I know, only Nikon Coolpix 775 is using this interface.
Mini B 8 pin circle
The picture on the left shows the Mini B 8Pin circular interface. Compared with the common types before, this kind of interface changes the original D-connector into a circular connector, and designs a bump to prevent wrong insertion. This connector can be found in some Nikon digital cameras, and CoolPix series is more common. Although Nikon has always insisted on using this interface, in some newer models, such as D 100 and CP2000, the most popular Mini B 5Pin interface is also adopted. Almost universal, 8Pin 2×4 interface: In addition to the Mini B 5Pin interface we have seen before, I think everyone must be familiar with the following interface, which was once quite popular.
Mini B 8 pin 2×4
As shown in the figure: Mini B 8Pin 2×4 interface, which is also a common interface. For example, we are familiar with iRiver's famous MP3 series, which is called "Iron Triangle" 180TC, and many other products in this series have adopted this interface. The application scope of this interface is still relatively wide, but after iRiver changed from 3XX series to Mini B 5Pin interface, this specification is obviously not as eye-catching as Mini B 5Pin. Edit this USB portable supplement standard USB portable supplement1.0: 20065438+0 65438+February. Usb Portable Supplement1.0a: It was released in June 2003, which is the current version. USB OTG is the abbreviation of USB On-The-Go and a technology developed in recent years. Published by USB implementer forum on February 8, 2000118, it is mainly used for data exchange between different devices or mobile devices. Especially PDA, mobile phone and consumer equipment. The development of USB technology brings inconvenience to the data exchange between digital cameras, video cameras, printers and other devices. The development of USB technology makes it possible for PC and peripheral devices to connect devices with various data transmission speeds in a simple way and at moderate manufacturing cost. All the applications mentioned above can be controlled by PC, as peripherals of PC, and exchange data through USB bus. However, this convenient exchange method, once you leave the PC, the device can't use the USB port to operate, because no slave device can act as a PC-like host. On-The-Go, that is, OTG technology is to realize data transmission between slave devices without a host. For example, the digital camera is directly connected to the printer, and through OTG technology, the USB ports seen by two devices are connected to print photos immediately; You can also send the data from the digital camera to the mobile hard disk with USB interface through OTG, so you don't need to carry expensive memory cards or portable computers for field work. In OTG products, some new functions have been added: * The new standard is suitable for designing compact connectors and cables; * On the traditional peripheral equipment, the host capacity is increased to adapt to point-to-point connection; * This ability can be dynamically switched between two devices; * Low power consumption, ensuring that USB can work under battery power supply. After using OTG, the connection between the original equipment and PC will not be affected, but there are more than 654.38 billion devices on the market with USB interfaces, which can also be interconnected through OTG. [ 1][2][3]
Introduction to USB 3.0
English1vbus (4.75-5.25v) vbus (4.4-5.25v)
Two-dimensional-two-
3 D+ D+
4 grounding grounding
USB signals are transmitted through twisted-pair wires marked with D+ and D- respectively, and half-duplex differential signals are used to jointly cancel the electromagnetic interference of long wires.
USB 2.0
USB is the abbreviation of English universal serial bus, which means "universal serial bus" in Chinese. It is a new interface technology applied in computer field. As early as 1995, there were personal computers with USB interface, but due to the lack of software and hardware support, the USB interface of these personal computers has been idle. After 1998, with Microsoft's built-in support module for USB interface in Windows 98 and the increasing number of USB devices, USB interface has gradually entered the practical stage. In recent years, with the popularity of a large number of personal computers supporting USB, USB has gradually become the standard interface of personal computers, which has become the general trend. On the host side, almost 100% of the latest personal computers support USB；; In terms of peripherals, there are more and more devices using USB interface, such as digital cameras, scanners, joysticks, tapes and floppy drives, imaging devices, printers, keyboards, mice and so on. The reason why USB devices are widely used mainly has the following advantages: 1, which is hot-pluggable. This makes it unnecessary for users to repeatedly "turn off the parallel or serial cable and then turn it on" when using external devices, but plug in the USB cable directly when the computer is working. 2, easy to carry. Most USB devices are small in size, light in weight and thin in thickness. For users, the same 20G hard disk, USB hard disk is half as light as IDE hard disk. When you want to carry a lot of data with you, of course, you will choose USB hard disk first. 3. Uniform standards. Everyone is familiar with hard disk with IDE interface, mouse and keyboard with serial port, printer and scanner with parallel port. But with USB, these application peripherals can be connected to the same standard personal computer, and then there are USB hard disk, USB mouse, USB printer and so on. 4. Multiple devices can be connected. USB often has multiple interfaces on personal computers, which can connect several devices at the same time. If a USB hub with four ports is connected, you can connect it again. Four USB devices, and so on, as far as possible, all the devices in your home can be connected to a personal computer at the same time, without any problems (note: 127 devices at most). However, why did USB2.0 appear again? What's the difference between USB 1. 1? Please don't worry, we'll talk about it later.
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