Why didn't the previous host have a USB interface?

There are few (1) interfaces, which limits the upgrade. (2) The connectors and cables in the chassis are staggered. (3) The operation is troublesome. (4) Speed is limited.

From 65438 to 0994, seven world-famous computer and communication companies, including Intel, Compaq, Digital, IBM, Microsoft, NEC and Nortel, set up USB forums. 1995 1 1 formally formulated the specification of USB 0.9 universal serial bus, and peripherals that truly meet USB technical standards began to appear in 1997. USB 1. 1 is the current standard 1999. At the Intel Developer Forum, participants introduced the USB 2.0 specification, which was supported by three new members, namely Hewlett-Packard, Lucent and Philips, in addition to Compaq, Intel, Microsoft and NEC.

2.USB definition

USB (Universal Serial Bus) is a technical standard for connecting external serial devices and an input/output interface standard for connecting computer systems and peripheral devices (such as keyboards, mice, printers, etc.). ). USB is a specification of home inspection. In USB mode, all peripherals are connected outside the chassis, and it is not necessary to open the chassis to connect peripherals. Allow hot-plug peripherals without turning off the power of the host. USB adopts "cascade" mode, that is, each USB device is connected to a USB socket of a peripheral with a USB plug and provides a USB socket for the next USB peripheral connection.

Through this daisy-chain connection, a USB controller can connect as many as 127 peripherals, but actually there are only11peripherals, and the distance (cable length) between each peripheral can reach 5 meters. USB can intelligently identify the insertion or removal of peripherals on the USB chain, which provides a good solution for the expansion of PC peripherals.

3.USB structure and connection mode

There are three transmission levels: low, medium and high. The USB port is a 7mm* 1mm jack with four signal lines: two for power supply and two for data transmission. USB system is mainly composed of host controller, USB hub and USB peripheral nodes, and the main structure of USB is mostly tree topology.

At present, there are two common USB interfaces, one is square and the other is flat. The former is usually called type A connector, and the latter is called type B connector. Both connectors have four pins, the middle two are used to transmit data, and the side two provide power for USB devices. The connector design is reasonable, and the user will not plug it wrong.

USB cable is divided into high-speed cable and low-speed cable. The transmission rate of high-speed cable is 12Mbps, which is mainly used to connect digital cameras. The transmission rate of low-speed cable is 1.5Mbps, which is mainly used to connect mouse and keyboard. The cable can provide 5V, 100 mA ~ 500 mA DC. Theoretically, there are 127 USB connections, but the maximum number of connections in the actual test is only11.

The USB specification divides USB into five parts;

(1) controller: it is mainly responsible for executing the commands issued by the controller driver;

(2) Controller driver: establish communication channel between controller and USB device;

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

(4)USB devices: including USB peripheral devices connected to PC, which are divided into two types: one type of devices can be connected to other USB peripheral devices, and the other type of devices cannot be connected to other peripheral devices; The former is called a hub and the latter is called a device. In other words, the hub has a USB port, which is used to connect other peripheral devices. Devices are equipment units that are connected to the computer to complete specific functions and conform to USB specifications, such as mice and keyboards.

(5) Device drivers: programs used to drive USB devices, usually provided by the operating system or USB device manufacturers, such as modem drivers and printer drivers. In addition, the USB standard also stipulates that the connection of all devices should not exceed 5 meters, which means that the outward length of all peripherals should not exceed 20 meters.

The latest Southbridge chip can only support five USB interfaces at most, so how will 127 USB peripherals be connected? There is a special USB peripheral-USB Hub (UH), which can connect 1 to 7 USB devices by using USB management chips with different capabilities. Acting as a relay station when the power socket is not enough is the key to realize the connection of multiple USB peripherals.

There are four transmission modes of USB (according to the different requirements of devices for system resources).

(1) Isochronous transmission mode: This mode is used to connect external devices that need continuous transmission and are extremely sensitive to time, such as microphones, speakers, telephones, etc. Isochronous transmission mode continuously transmits data between the host and USB devices at a fixed transmission rate. When there are errors in data transmission, USB will not handle these errors, but continue to transmit new data.

(2) Interrupt transmission mode: The amount of data transmitted in this mode is very small, but these data need to be processed in time to achieve real-time effect. This mode is mainly used for keyboard, mouse, game machine and other external devices.

(3) Control transmission mode: This mode is used to handle the data transmission of the host USB device. Include equipment control instruction, equipment status inquiry and confirmation command. When the USB device receives these data and commands, it will process the data arriving in the queue according to the first-in first-out principle.

(4) Batch transmission mode: This mode is used to transmit data requiring correctness. Usually printers, scanners and digital cameras are connected to the host in this way. Among the four data transmission modes, except the isochronous transmission mode, the other three modes will try to retransmit the data when there is an error in data transmission to ensure its accuracy.

Comparison of advantages and disadvantages of USB

Advantages of USB interface disadvantages of USB interface

The advantages and disadvantages of USB are low, and the communication efficiency between devices is low.

Simple and fast connection, strong compatibility and good expansibility.

High speed, the transmission speed of USB2.0 interface is as high as 480Mbps, and the length of more than 4000 times serial port connection cable is relatively short.

The reason why USB can't be popularized in the early stage

There is no obvious difference between 1.USB peripherals and traditional peripherals.

2. No interface space is reserved (occupied by the traditional serial communication interface and LPT printer), and the card needs to be transferred through USB.

3. Insufficient operating system support

4.ATX motherboard was not born.

The concept of USB file is too abstract.

Fully understand USB 2.0 standard.

USB 2.0 (Unified Serial Bus) is a computer peripheral connection specification, which was jointly formulated by a series of PC industry leaders such as Compaq, Hewlett-Packard, Intel, Lucent, Microsoft, NEC and Philips. USB2.0 adds a high-speed data transmission mode to the current USB 1. 1 specification. In USB2.0, in addition to the two modes of1.1.5Mbit/s and 12Mbit/s specified in USB1,a "high-speed" mode of 480Mbit/s(60MB/s) is added.

At present, the USB 1. 1 specification is widely used, and its speed (12Mbps) is about 0/00 times faster than that of the standard serial port, which supports the simultaneous connection of multiple devices and has a real "plug and play" feature. Due to these advantages, USB is widely favored by peripheral manufacturers. After more than two years of promotion, USB specification has been widely used in digital products such as computers, game machines and audio-visual appliances. The transmission speed of the new "USB 2.0" specification is 40 times faster than the current "USB 1. 1" version.

The realization of USB2.0 needs the support of both hardware and software. In addition to the host controller and other devices installed in the computer and the control chip built in the hub, it is necessary to support version 2.0 and install driver software in the operating system. The control chip supporting USB2.0 has been commercialized. Operating systems supporting USB2.0 will also be launched at about the same time.

USB Implementers Forum, the standardization organization of USB, has published the operation guarantee signs of LSI, peripheral devices and components of USB2.0, which are only allowed to be used by products tested by certification bodies. USB 2.0 is an interface specification with data transmission speed up to 480 mbit/s.

The first batch of certified products are the main controller LSI developed by NEC and the PCI bus board using this LSI developed by Orange Micro.

At the same time, the USB implementer forum has also changed the logo that proves that the product supports USB 1. 1. The new logo removes the part of the USB2.0 logo that says "high speed".

As early as last August, Promoter Group announced a USB2.0 speed range at the Intel Developer Forum: between 360 and 480 Mbps. After several months of careful consideration, the speed was finally set at 480Mbps. Obviously, this is not an imaginary number. Through a lot of research and testing of semiconductor technology, engineers found that at this speed, not only the production process is no problem, but also it can maintain complete compatibility with USB 1. 1.

VIA's VT6202 control chip of USB2.0 standard supports four USB2.0 interfaces, with the highest transmission speed of 480Mbps, based on PCI slots.

USB 1. 1 and USB 2.0

The development speed of computer hardware is very fast, and the development speed of its peripherals is an obvious example. Keyboards, mice, modems, printers and scanners have long been well known, and cameras, digital cameras, MP3 players, external hard disks and CD-ROMs have followed. Where can so many devices be connected? USB interface came into being. USB is called universal serial bus, which means universal serial bus. It standardizes the connection of computer peripheral devices, and has the advantages of supporting hot plug, safely connecting or disconnecting devices when starting up, and realizing real plug and play. No need for external power supply, one mouth is multi-purpose, no matter how many devices are connected.

Almost all motherboards have more than two USB standard interfaces, and more peripherals support USB, such as USB keyboard and mouse, USB modem, USB speaker, USB printer, USB scanner, USB joystick, USB Hub, USB monitor, USB digital camera, USB camera and USB external hard disk. At present, the universal USB specification is USB 1. 1, and the standard interface transmission rate of USB 1 is 12Mbps, which can theoretically support 127 devices. Connect multiple peripheral devices through USB HUB, that is, USB expander. The maximum length of connecting cable is 5 meters, which is enough for general devices. Speaking of USB 1. 1 standard interface transmission rate, I have to say a few more words. Many people misunderstand "12MBPS" as 12 Mbps. Actually, this is not right. If it takes only 60 seconds to transmit data of 720M (the capacity of a CD) at the speed of 12M/s, this speed is probably faster than that of ordinary hard disk. ! Actually, "12MBPS" should be 12 Mbps or 12 Mbps, which is equal to1.5mbps.. See the difference. This should start with bit and byte: both of them are translated into "bit", which is the unit of data measurement, bit= bit, byte= byte, octet, that is, 1byte=8bits, and the conversion between them is 1: 8. MBPS = megabit/s (megabit/s or megabit/s) is the unit of speed, MB = megabit/s (megabit/s) is the unit of quantity, 1MB/S (megabit/s) =8MBPS (megabit/s) is very clear now, so don't be referred to by JS (profiteer). 1.5MB/S is acceptable, but it is far from12mb/s. 1.5MB/S is enough for most USB devices, but if you use a USB hard disk with a capacity of 30GB, you need at least/kloc to copy 10GB data from the hard disk. In fact, the speed of USB interface is only about 1.0MB/S, which is enough for general USB devices. But it takes at least 2.84 hours to copy 10GB data from your hard disk, and during this time, your CPU and hard disk are too busy to do anything else, so you have to wait. Although this is an extreme situation, it also reveals that the transmission rate of USB interface needs to be further improved. Now, the newly released USB2.0 standard is exactly what we want.

The USB2.0 specification is developed from the USB 1. 1 specification. Its original goal was to increase the transmission rate of USB1.1(12 Mbps) by 10-20 times, but it actually increased by 40 times, reaching 480mbps, which was converted into 60 MB. Compared with USB 1. 1, USB2.0 is a qualitative leap. It is satisfactory that USB2.0 and USB 1. 1 can be compatible with each other, that is, USB2.0 devices can work on USB 1. 1 interface, and vice versa. Of course, the speed of USB 1. 1 devices will not be improved by being installed on the USB2.0 interface, and the speed of USB2.0 devices also installed on the USB 1. 1 interface will be limited to12 Mbps (1.5mb). USB2.0 and USB 1. 1 use the same connecting cable and port. When Intel made a presentation at the Intel Developer Forum in April this year, it connected a USB2.0 scanner and a USB 1. 1 printer to a computer at the same time, and successfully used the scanner to input a page of press release into the computer and printed it out with the printer.

So, when buying USB devices, do you have to choose USB2.0 first? This depends on your specific situation. First of all, the USB interface of your motherboard should support the USB2.0 specification. Secondly, it depends on whether USB2.0 is necessary for you. The transmission rate of 60MB/S is only a theoretical value, and it is also limited by the system environment (CPU, hard disk, memory, etc.). In the end, you just need to spend more money (new things are definitely more expensive).

Looking forward to the future, we hope that USB2.0 can develop rapidly, and we also hope that manufacturers can develop more products supporting USB2.0 as soon as possible to meet the urgent needs of users.

Compared with USB 1. 1.

At present, most PCs are equipped with USB functions (motherboards usually provide two USB ports, and some high-end monitors even provide USB adapters, increasing the total number of USB ports to more than four), and peripherals (such as scanners, webcams, digital cameras, etc.) are also increasing. ) USB interface is used in the market, and the price is not expensive, so the traditional input/output devices are less and less optimistic. With the appearance of USB 2.0, the input/output bandwidth has been significantly expanded, which will further stimulate the development of USB peripherals.

With the introduction of new standards, users can immediately enjoy faster broadband Internet connection, higher resolution video conference cameras, next-generation printers and scanners, and faster external storage devices. In addition, USB 2.0 can make the existing technology play a higher efficiency. For example, using a USB 2.0 digital camera, you can download a "roll" of digital film in a few seconds, while the early USB version took several minutes; Within one minute, 1GB data can be backed up from PC hard disk to portable storage device through USB 2.0, while USB 1. 1 takes half an hour. Scanners can scan high-resolution digital images in a few seconds through USB 2.0, while USB 1. 1 takes several minutes.

Compared with IEEE 1394.

The main difference between them lies in their respective applications. USB 2.0 is mainly used to connect PC peripherals, while IEEE 1394 is mainly located in the audio/video field, which is used to manufacture consumer electronic devices, such as digital VCRs, DVDs and digital TVs. In the future, USB 2.0 and IEEE 1394 should coexist in many consumer systems.

Nowadays, more and more PCs provide USB function, and a large number of USB peripherals that can be connected with PCs appear on the market. Therefore, the speed of USB is naturally required to be further improved to prepare for the comprehensive popularization of USB peripherals. In the field of audio-visual consumer appliances, IEEE 1394 has become the de facto connection standard. Therefore, the future PC must meet the IEEE 1394 standard if it wants to connect with this kind of electrical appliance.

According to the data, the transmission speed of "USB 2.0" is 480 Mbps per second, which is faster than IEEE 1394. The second version of USB 2.0 will reach the speed of 800 Mbps (the highest ideal value is 1600 Mbps), which will become the highest transmission standard beyond IEEE 1394. In addition, "USB 2.0" is compatible with all current "USB 1. 1", and the unit cost is cheaper than IEEE 1394, so international computer manufacturers led by INTEL, COMPAQ and HP all support "USB 2.0".

In contrast, IEEE 1394 will be less attractive. Because the IEEE 1394 interface specification developed from Apple's FireWare interface and became a universal international standard, Intel is very clear. Although there is no way to openly oppose it, it will certainly not be too supportive. Therefore, Intel's chipset has released a number of products, but it has always hidden its support for IEEE 1394. To tell the truth, the 1394 device has not developed so far, which has something to do with Intel's support.

It seems that the prospect of IEEE 1394 is not very optimistic. Although manufacturers have introduced some motherboards or products with 1394 interface, the number is really small, which can hardly become a big climate. Moreover, there are newer interface forms-simpler and higher-speed serial ATA interface, so the future peripheral interfaces should be USB2.0, IEEE 1394 and serial.

Microsoft Windows XP, which was listed as early as 200 1. 10, supported USB2.0, which once again inspired the USB camp. Although the launch date of Intel South Bridge chip ICH3 (supporting USB2.0) is still uncertain, all peripheral chips and products have been ready for a long time based on the popularity and share of USB in PC and the improvement of functions (the transmission speed is increased from 12Mbps).

Recently, with domestic manufacturers receiving OEM orders from international manufacturer Pocket PC, there has been a PDA craze in Taiwan Province Province. SHD(Smart Handheld Device) seems to be the only light that can be seen in the IT industry in Taiwan Province Province in the post-PC era, and it is also a relatively substantial product that IA products echo in Taiwan Province Province. Whether it's PDA, DSC, MP3 or even mobile phone, thinness and thinness have become the general trend, and data transmission is gradually converted into USB interface. When universal USB connector can't meet the needs of institutions, Mini USB connector becomes the best substitute.

It is reported that Lien Chan Technology is the only connector manufacturer in China that has passed the full series (8 groups) test and obtained USB2.0 certification, and participated in the formulation of the next-generation USB interface Mini USB specification. At present, a full range of products have been developed and obtained USB2.0 certification. Wen Dixing of Lien Chan Science and Technology Products Department pointed out that after more than half a year's promotion, Mini USB connector has been widely recognized and selected by customers, including digital cameras from Japan and Hewlett-Packard, Compaq PDA, Symbol barcode scanner, and related domestic industrial manufacturers. If we add the cellular phones being developed by Motorola, Qualcomm and other mobile phone manufacturers, it is expected that the demand will continue to heat up this year, and there will be opportunities to challenge the monthly 1 10,000 units in the third quarter. Wendy further stated that although Mini USB is an international standard specification, it refers to the compatibility between products, and Lien Chan has many institutional patents because he participated in the formulation of specifications and launched a series of products very early. If competitors deliberately copy and imitate, Lien Chan's claim to intellectual property rights will definitely be actively maintained and never relaxed.

Lien Chan has been committed to the research and development and manufacturing of connectors for many years, and has been recognized by the industry in the research and development and manufacturing technology of high-precision products such as fine spacing, high frequency and surface bonding. It is also because we have mastered the core technology of connector development and made special consideration in material selection, and finally won the favor of USB-IF, giving Lien Chan the opportunity to participate in and lead the formulation of Mini USB connector specifications. In the future, Lien Chan will not only continue to develop products with finer spacing and higher frequency, but also provide customers with good solutions to high-frequency problems such as crosstalk, time delay, impedance matching and attenuation. In addition, in the development of fully automatic technology, most fully automatic or semi-automatic fixtures are developed by themselves according to the characteristics of various products; USB, 1394 and communication products have been put into automatic production, which ensures the yield and cost of production and lays a competitive advantage in price, delivery and quality. In the future, we will continue to develop, innovate and improve fully automatic and semi-automatic fixtures/processes.

Wendixing pointed out that under the condition that subjective and objective conditions are gradually mature, it is expected that in the second half of this year, optical USB2.0 and Mini USB connectors will account for nearly 20% of the company's revenue, and Lien Chan's market share and leading position will be more stable.

USB2.0 hub appears at a high price.

The new generation USB2.0 standard can reach the transmission speed of 480Mbps, so it can be used not only to connect various USB peripherals, but also to build a USB-based LAN. ATEN International recently released a USB2.0 hub, which is very compact and has six USB2.0 interfaces, and no external power supply is needed.

Introduction of USB and USB 2.0

From the Intel HX, TX, VA chipset at the end of 1994, a device interface with USB interface appeared, and then it was quickly supported by Win95 (officially supported by MS Win95 OSR2). The specification of USB is made by Intel, NEC, Compaq, DEC, IBM, Microsoft and Nortel. When all serial ports and PS/2 interfaces are replaced by USB interfaces in the next few years, the speed of input devices will be much faster. What will happen?

What about IEEE 1384, which has been competing with USB? Will USB unify the peripheral interface? After all, there are many USB products on the market now, but it is very difficult to unify the market. Now the appearance of USB 2.0 specification may let us see the future of USB device interface.

USB 1.0/ 1. 1/ 1 . x

In the version of USB1.0/1.1.2, the interface speed of USB is always unsatisfactory, which is12mb/s (12mb/s-/kloc-. The speed of other equipment directly operated by the machine is calculated at tens of megabytes or even hundreds of megabytes per second, which is only 1.2 MB/s, which can be ignored at all. It was not until February that USB 2.0 specification appeared in 1999 that the situation changed. Its speed far exceeds 400Mb/s of IEEE 1394, reaching 480Mb/s(60Mb/s), making it a new interface completely free from the existing restrictions.

Resource occupation

The USB interface no longer uses IRQ interrupt control and I/O address resources, but relies on the operating system to allocate a logical location for data transmission after the device is turned on, so it can be greatly expanded and can connect 127 peripheral devices. If so, the power supply becomes a problem. When there are too many devices, the devices cannot be driven due to load problems, and only one external power supply can ensure the normal use of 127 I/O devices. In order to ensure that the transmission process does not consume too much power supply voltage, the USB specification stipulates that the wiring of the device should not exceed 5 meters, and the USB device is also designed with low power consumption between 3.3 V and 5 V-5 V (the high power consumption device is designed as an external power supply).

There are many USB interface products, keyboard, mouse and camera are the most common, and now there are more and more scanners and printers. Modern USB Hub, game machine, TV box, floppy drive, CD-ROM drive, CDRW, hard disk, and even sound card, speaker, mobile phone charger, read-write electronic board and network card have all appeared. Some of these devices use full-speed mode (FS: 12mb/s) and low-speed mode (LS: 1.5mb/s). For example, mice and keyboards are low-speed devices, while printers and scanners operate in full-speed device mode.

USB is much faster than serial communication interface, and the purpose of this standard is to replace serial communication interface. Parallel communication interface is also the target that USB will replace, which is only a little slower than today's parallel communication interface, but USB has great advantages in user-friendly interface.

USB 1。 X has become the standard data communication configuration of PC and MAC, and this interface has been adopted by manufacturers, users and PC OEM. At present, we see that many devices on the market have a shortcoming, which is the speed of these USB devices. The appearance of USB 2.0 gives us new hope.

What is USB 2.0?

Compaq, Hewlett-Packard, Intel, Lucent, Microsoft, NEC and Philips jointly formulated the product specification of USB 2.0. USB2.0 improves the data transmission speed between devices to 480Mbps, which is 40 times faster than USB 1.x, but the initial speed of USB 2.0 was only defined as 240Mbps, but the technical team tried to improve the speed to 480Mbps. The biggest advantage of speed increase for users is that users can use more efficient external devices, and peripherals of various speeds can access USB 2 lines, unlike the USB 1.x era, because of the high bandwidth, more devices do not have to worry about the bottleneck effect in data transmission. On the premise of high speed, the excellent characteristics of USB 1. X, and ensure backward compatibility.

Impact on users

USB 2.0 is similar to USB 1.x, but the bandwidth is higher. USB 2.0 can use cables with the same specifications in the original USB definition, and the connector specifications are exactly the same. Moreover, when the new USB 2.0 compatible devices are used together, they will not conflict with USB 1.x devices. At present, products with USB 2.0 specifications have begun to appear, including 8X4X32 CDRW and new USB hard disks. The new VIA chipset, Intel, AMD, SIS and Ali all added support for USB 2.0 to their new products in the second quarter. It is rumored that the chipset of Intel B-Setp will support USB 2.0, but there is no sample yet. It seems that only ICH3 will join the USB 2.0 specification. It must be noted that USB 2.0 products cannot run on the interface of USB 1 except specially designed compatible hardware. X even if they are designed as low-speed products. On the contrary, USB 2.0 interface comes from backward compatibility, which can completely deal with all kinds of USB 1.x products.

Is Windows Ready for USB 2.0?

In terms of software, the operating system fully supports USB 1. X For USB 2.0, the system can recognize and work normally, but USB 2.0 can't give full play to its performance advantages. After the system detects a USB 2.0 device, it will prompt you that your USB device needs to be optimized. At present, we haven't fully supported the WINDOWS system of USB 2.0, but we have advanced in LINUX, MACOS and BEOS, and all of them have related software support or system packages. But what is certain is that when USB 2.0 products appear, Windows will catch up quickly. Now WINDOWS XP will fully support USB 2.0 devices, but when the system motherboard supports USB 2.0, Microsoft should soon launch a patch for USB 2.0.

Main characteristics of USB2.0 specification

quick

The transmission speed of the interface is as high as 480Mbps, which is more than 4,000 times of the serial port speed compared with the serial port speed of 1 15200bps, and can fully meet the requirements of peripherals that need a lot of data exchange.

Simple and fast connection

All USB peripherals can be connected to the computer simply and conveniently through universal connectors, and the installation process is highly automated, and hot plug can be realized without opening the chassis card, considering resource allocation and turning off the computer power.

No external power supply is required.

As we all know, some devices with common serial or parallel ports, such as printers and scanners, need corresponding external power supply system, and USB power supply can provide 5V power supply for low-voltage devices, so new devices do not need special AC power supply, thus reducing the cost of these devices and improving the cost performance ratio.

There are different bandwidths and connection distances

USB provides low-speed and full-speed data transmission speed specifications. When transmitting at full speed, the connection distance between nodes is 5m, and 4-core cables (2 power lines and 2 signal lines) are used for connection. This rate is 100 times faster than the standard serial port and nearly 10 times faster than the standard parallel port. So USB can support high-speed interfaces (such as ISDN, PRI, T 1, etc. ), so that users have enough bandwidth to buy new digital peripherals.

Support multi-device connection

Ports are expanded in daisy chain, which avoids the limitation of the number of slots for expanding peripherals on PC and reduces the number of I/O interfaces on PC.

Provide two-way data support for telephone.

USB can support asynchronous and synchronous data transmission, so that mobile phones can be integrated with PC and share voice mail and other functions.

High definition audio.

Because USB audio information is generated outside the computer, it reduces the chance of electronic noise interfering with the sound quality, thus making the audio system have higher fidelity.

Good compatibility

USB interface standard has good backward compatibility. Take USB 2.0 and 1. 1 as examples. Version 2.0 can be well compatible with previous USB 1. 1 products. When the system automatically detects the interface type of 1. 1, it will automatically transmit at the previous speed of 12Mbps, while other 2.0 devices will not slow down because they are connected to a standard 1. 1, and can still transmit at the speed specified by standard 2.0.

What products are there for USB interface?

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Usb1.0/1.11.2 specification list USB 2.0 specification list.

High speed12mb/s; Low speed 1.5 MB/ s

127 supported devices

The length of the connecting wire shall not exceed 5m.

The rated voltage is 3.3V-5v (500mA).

The chipset supports Intel VX/HX/TX and higher versions; SIS 5595 and above; Ali m1431; Through MVP3

The system supports Win95 OSR2, MACOS/8, Linux 3.0 and BeOS Windows XP.

USB is plugged into optical drives, hard disks and other devices, which requires a lot of power. Generally, mice and the like don't consume much power.