USBIs an externalBus standard, standardize computer andperipheralConnection and communication.USB interface hasHot plugFunction.USB interface can connect a variety of peripherals, such as mouse and keyboard.USB was created byIntelAfter being jointly launched in 1996, many companies have successfully replaced serial ports andParallel port, has become today's computer andIntelligent deviceRequired interface of.After years of development, the USB version has developed into the USB4 version.For mostengineerFor example, developUSB2.0The main obstacle of interface products lies in: facing complexUSB2.0Protocol, self writtenUSB deviceOfDriver, familiar withsinglechipProgramming of.This requires not only considerable VC programming experience, but also the ability to write USB interface hardware (firmware) programs.So most people give up developing USB products themselves.
development history
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USB 1.0
Figure 1
USB 1.0 was introduced in 1996, and its speed is only1.5Mb/s(Bits per second)； In 1998, it was upgraded to USB 1.1, and the speed was greatly improved to12Mb/sThis standard interface can also be seen on some old devices.USB1.1It is a common USB specification, and its high-speedtransmission speed by12Mbps, the transmission rate of low speed mode is1.5Mbps(b means Bit), b/s generally means bittransmission speed , bps meansBit transfer rate, equal in value.B/s and b/s,BPS(bytes per second) cannot be confused with bps (bits per second).1MB/s（Megabyte/Seconds)=8Mbps（Megabit/Second), 12Mbps=1.5MB/s, most MP3s are of this typeInterface type。[2]As shown in Figure 1.
The USB2.0 specification is evolved from the USB1.1 specification.Its transmission rate reaches 480Mbps, which is converted to 60MB/s, enough to meet the rate requirements of most peripherals.USB 2.0Enhanced Host Controller Interface in（EHCI）A USB 1.1 compatible architecture is defined.It can use USB 2.0 drivers to drive USB 1.1 devices.In other words, all devices supporting USB 1.1 can be directly used on the USB 2.0 interface without worryingcompatibilityThe problem. Accessories such as USB cable and plug can also be used directly.[2]
The change brought by the use of USB to the printer application is a significant increase in speed. The USB interface provides a connection speed of 12Mbps, which is more than 10 times faster than the parallel port speed. Under this speed, the transfer time of printed files is greatly reduced.The USB 2.0 standard will furtherInterfaceThe speed is increased to 480Mbps, 20 times the speed of ordinary USB, which greatly reduces the transfer time of printed files.[2]
IntelMicrosoft、HP、Texas Instruments、NEC、ST-NXP and other industry giantsUSB 3.0Promoter Group announced that the new generation USB 3.0 standard developed by the organization has been officially completed andPublic release。USB 3.0Theoretical speedAt 5.0Gb/s, it can only reach 50% of the theoretical value, which is close to 10 times of USB 2.0.USB3.0Ofphysical layer8b/10bCoding methodThe calculated theoretical speed is 4Gb/s,Actual speedThe protocol overhead should also be deducted, which is less than 4Gb/s.Widely used for PC peripherals andConsumer Electronics。[2]
USB 3.0 will be called "USB SuperSpeed" in actual device applications, conforming to the previous USB 1.1 FullSpeed and USB 2.0 HighSpeed.It is expected that commercial controllers supporting the new specification will be available in the second half of 2009,Consumer gradeThe product has been launched.[2]
USB 3.1 Gen2 is the latest USB specificationIntelAnd other companies.Data transmission speedThe speed can be increased to 10Gbps.AndUSB 3.0(i.e. USB 3.1 Gen1) technology, the new USB technology uses a more efficient datacoding system , and provide more than twice the effectivenessthroughput rate 。It's completelyBackward compatibilityExisting USB connectors and cables.
USB 3.1 Gen2 is compatible with existing USB 3.0 (i.e. USB 3.1 Gen1) software stack and device protocol, 5GbpsHubAnd equipmentUSB 2.0Products.
USB-IFThe latest USB naming convention, the originalUSB 3.0andUSB 3.1It will no longer be named. All USB standards will be called USB 3.2. In consideration of compatibility, USB 3.0 to USB 3.2 are called USB 3.2 Gen 1, USB 3.2 Gen 2, and USB 3.2 Gen 2x2 respectively.
USB 4.0
The USB4.0 specification was released by the USB Implementers Forum on August 29, 2019.USB4 is based onThunderbolt3 Agreement.It supports 40 Gbit/s throughput, is compatible with Thunderbolt 3, andBackward compatibilityUSB 3.2 and USB 2.0.[8]
Main advantages
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USB devices have the following advantages:[1]
1. YesHot plug。When using an external device, the user does not need to turn off the computer, but directlyUSBPlug in for use.[1]
2. Easy to carry.USB devices are mostly "small, light and thin". It is convenient for users to carry a large amount of data with them.Of course, USB hard disk is the first choice.[1]
3. Unified standards.The common thing isIDE interfaceWith USB, these application peripherals can all use the same standards aspersonal computerConnect, then there are USB hard disk, USB mouse, USB printer, etc.[1]
4. Multiple devices can be connected.USB often has multiple interfaces on personal computers, which can connect several devices at the same timeUSB HUBCan be connected again;Four USB devices, and so on, can be connected as far as possible, and all the devices in your home can be connected to a PC at the same time without any problem (Note: up to 127 devices can be connected).[1]
Interface layout
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USBIt is a common PC interface. It has only four wires, two power supplies and two signals, so the signal isSerial transmissionThe usb interface is also calledSerial port，usb2.0Its speed can reach 480Mbps.It can meet various industrial and civil needs.[3]
USB interfaceoutput voltage And current:+5V, 500mA.In fact, there is an error, which cannot exceed+/-0.2V at most, that is, 4.8-5.2V.The four wires of the USB interface are generally allocated as follows. It should be noted that the positive and negative poles must not be reversed, or the USB device or computer will be burnedNanqiao chip: black line: gnd;red thread:vcc；Green line：data+ ；White line: data -.[3]
With the popularization of various digital devices, especially MP3 andDigital cameraWith the popularization of USB, 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 identical.These data lines are the same at one end of the PC, but when connecting to the device end, different interfaces are usually used for volume considerations.The following is a brief introduction to the various applications of the Mini sub interface.[2]
B-5Pin
Mini B 5Pin
This interface can be said to be the most common interface. Because of its excellent anti misplug performance and small size, it is gaining more and more attention from manufacturers. Now this interface is widely availablecard reader, MP3, digital camera andmobile hard disk driveOn.[2]
Another form of Mini B 4Pin is Mini B 4Pin Flat.As the name implies, this interface is more flat than the Mini B 4Pin and is widely used in devices.[1]
B-8Pin
Mini B 8Pin Round
Mini B 8Pin Round data cable
Compared with the previous ordinary type, this type of interface changes the original D-type connector into a round connector, and a bulge is designed to prevent accidental insertion on one side.[2]
This kind of joint can be seen in someNikonOfDigital camera，CoolPixThere are many series.althoughNikonThis interface has always been used, but some newer models, such as the D100 and CP2000, also use the most popular Mini B 5Pin interface.[2]
B-8Pin-2×4
Mini B 8Pin 2 × 4
This interface is also a common interface, such asiRiverThe famous MP3 series of“Iron triangle”180TC and many other products in this series use this interface.This interfaceScope of applicationIt's also quite wide, but fromiRiverSince the 3XX series has been fully replaced with the Mini B 5Pin interface, this specification is obviously less eye-catching than the Mini B 5Pin.[2]
Micro USB
Micro USB 2.0 B port
Comply with USB2.0 specification and support 12Mbit/sData transmission rate。The module controls the pins according to the Microport interface, which is convenient to connect with themain controller to be connected.[4]
Type-C is a new form of USB interface, which is accompanied by the latestUSB 3.1Standard came into being.fromUSB-IFIt was released by the organization in August 2014. It is USBStandardization OrganizationIn order to solve the long-term physical problems of USB interfaceinterface specification Not unified, electric energy can onlyOne way transmissionIt is a new interface developed for charging, display,data transmissionAnd other functions.The biggest feature of Type-C interface is that it supports insertion in both positive and negative directions, formally solving the worldwide problem of "USB can never be inserted".[6]
TYPE-CHardwareInterfaceIt has obvious characteristics, mainly including the following points:[6]
(1) It supports positive and negative symmetric plugging, and solves the problem that reverse plugging cannot be inserted in practical applications;[6]
(2) The thin interface can support thinner devices, which canPortable equipmentIs thinner and smaller;[6]
(3) Support higher power transmission, up to 100 watts, and support more high-power load devices.[6]
(5) It supports two-way power transmission, both power transmission and power receiving.[6]
TV application
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Different functions
USB 3.0 male
Although many TV sets are equipped with USB interface, they are connected through USB interfacestorage deviceThe functions that can be realized later are different.Some TVs only support playing pictures from USB storage devices, while others can play music files and videos in specific formats.[7]
USB line
Speaking of USB playback capability, the current domestic TVs are still excellent in USB playback capability,H.264Coding and RM/RMVB formatOfHD videoGenerally, it can play smoothly, although the effect is better than that of high-endHD Player There is still a gap, but it is enough for ordinary users to use.[7]
TV USB interface
TV USB interface
The USB interface on the TV side is shown in Figure 2 below, which can be directly connectedUSB driveperhapsmobile hard disk drive。[7]
