What is USB? Composition of USB interface USB protocol simulation

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What is USB? Composition of USB interface USB protocol simulation

Posted Date: 2024-01-13

What is USB

USB (Universal Serial Bus) is a serial bus standard and a technical specification for input and output interfaces. It is widely used in information and communication products such as personal computers and mobile devices, and has been extended to photographic equipment, digital TVs (set-top boxes), game consoles and other related fields. The latest generation is USB4, with a transmission speed of 40Gbit/s, a three-stage voltage of 5V/12V/20V, and a maximum power supply of 100W. The new Type C interface allows blind plugging of the front and back.

USB development history


USB 1.0

USB 1.0 appeared in 1996, with a speed of only 1.5Mb/s (bits per second); it was upgraded to USB 1.1 in 1998, and the speed was greatly increased to 12Mb/s. This standard can still be seen on some old devices interface. USB1.1 is a more common USB specification, with a high-speed transmission rate of 12Mbps and a low-speed transmission rate of 1.5Mbps.


USB 2.0

The USB2.0 specification evolved from the USB1.1 specification. Its transmission rate reaches 480Mbps, which is 60MB/s converted into MB, which is enough to meet the rate requirements of most peripherals. The Enhanced Host Controller Interface (EHCI) in USB 2.0 defines an architecture that is compatible with USB 1.1. It can drive USB 1.1 devices with USB 2.0 drivers. In other words, all devices that support USB 1.1 can be used directly on the USB 2.0 interface without worrying about compatibility issues, and accessories such as USB cables, plugs, etc. can also be used directly.

The change brought by using USB to printer applications is a substantial increase in speed. The USB interface provides a connection speed of 12Mbps, which is more than 10 times faster than the parallel port. At this speed, the printing file transfer time is greatly reduced. The USB 2.0 standard further increases the interface speed to 480Mbps, which is 20 times the speed of ordinary USB, significantly reducing the transmission time of printing files.


USB 3.0

The USB 3.0 Promoter Group, composed of industry giants such as Intel, Microsoft, HP, Texas Instruments, NEC, ST-NXP and other industry giants, announced that the new generation USB 3.0 standard developed by the organization has been officially completed and publicly released. The theoretical speed of USB 3.0 is 5.0Gb/s, but in fact it can only reach 50% of the theoretical value, which is close to 10 times that of USB 2.0. The physical layer of USB3.0 uses 8b/10b encoding, so the theoretical speed calculated is only 4Gb/s. The actual speed will also deduct the protocol overhead, which is less than 4Gb/s. Can be widely used in PC peripherals and consumer electronics.

USB 3.0 will be called "USB SuperSpeed" in actual device applications, following the previous USB 1.1 FullSpeed ​​and USB 2.0 HighSpeed. Commercial controllers supporting the new specification will be available in the second half of 2009, and consumer products are already on the market.


USB 4.0

The USB4.0 specification was released by the USB Implementers Forum on August 29, 2019. USB4 is based on the Thunderbolt 3 protocol. It supports 40 Gbit/s throughput, is Thunderbolt 3 compatible, and is backwards compatible with USB 3.2 and USB 2.0.

Composition of USB interface

The USB interface consists of cables, connectors, and protocols.


cable:A USB cable is a cable used to transmit data and power, usually in a twisted pair structure. USB2.0 and previous standards use 4 wires, namely two data wires (D+ and D-) for data transmission, one VCC wire for power supply, one GND for ground wire USB3.0 and Later standards introduced multiple ultra-high-speed differential transmission lines for data transmission.


Connector:There are many types of USB connectors for different devices. Common connectors include standard type A and B, small type A and B, mini type A and B, etc. The USB connector is designed to be highly compatible and can be inserted in any direction without distinguishing the front and back.


protocol:The USB protocol specifies the format and sequence of data transmission. USB transmission uses an asynchronous communication method based on the host-device mode. The host initiates data transmission and requests the device to respond and transmit data when needed. The USB protocol supports multiple transfer modes, including control transfer, bulk transfer, interrupt transfer and isochronous transfer.

USB advantages

USB devices mainly have the following advantages:

Can be hot swapped

When using external devices, users do not need to turn off and on the computer. Instead, they can directly plug in the USB and use it while the computer is working.

Easy to carry

Most USB devices are known for being "small, light, and thin", which is very convenient for users to carry large amounts of data with them. Of course, USB hard drive is the first choice.

Unified standards

The most common ones are IDE interface hard drives, serial port mouse and keyboard, and parallel port printers and scanners. But with USB, these application peripherals can all be connected to personal computers using the same standards. Then there are USB hard drives, USB Mouse, USB printer, etc.

Can connect multiple devices

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, four more USB devices can be connected, and so on, as many connections as possible. Connect all your home devices to one PC at the same time without any problems (Note: Can connect to up to 127 devices).

SIDesigner simulation demonstration

The following takes USB signal SerDes transmission as an example to demonstrate the Julin tool SIDesigner.

The schematic diagram of the construction is as follows:

Set parameters and view simulation output results:

SIDesigner provides a very convenient measurement method, such as eye height and eye width:

Review Editor: Liu Qing

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