USB is a new generation interface standard jointly introduced by world-famous computer and communication companies. The full name of the USB is Universal Serial Bus. It is a fast and flexible bus interface. Communications standards were developed to resolve the contradiction between the increasing number of PC peripherals and the limited slots and connectors on the motherboard.
USB is broadly divided into low-speed USB, high-speed USB, high-speed USB, and super high-speed USB, corresponding to USB1.0, USB1.1, USB2.0, USB3.0 , and USB3.0 is divided into GEN1, GEN2, etc. The latest generation is USB4, with a transmission speed of 40Gbps, a three-level voltage of 5V/12V/20V, and a maximum power supply of 100W. The new type- C interface allows blind plugging in from front and back.
USB Certified Mark
Historage of USB
| Designer | Compaq, DEC, IBM, Intel, Microsoft, NEC, and Nortel |
| Date | 1994 |
| Manufacturer | Intel, Compaq, Microsoft, NEC, Digital Equipment Corporation, IBM, Nortel |
| Predecessor | Serial interface, parallel interface, game port, Apple Desktop Bus, PS/2 interface |
General Specification of USB
| Length | 5m (Max) |
| Width | 11.5mm (Type A connector), 8.45mm (Type B connector) |
| Height | 4.5mm (Type A connector), 7.78mm (Type B connector, pre-v3.0) |
| Hot Plug | Supported |
| External | Supported |
| Cable | Four cables, while USB 3.0 has nine cables |
| Pin | 4 (1 power supply, 2 data, 1 ground); USB 3.0 has nine (another four are supplied to SuperSpeed technology); USB 3.1 Type-C has 24 devices |
| Connector | Single |
Data of USB
| Data Signal | Data packets defined by the specification |
| Width | 1 bit |
| Bit Rate | 1.5/12/480/5000/10000/20000/40000 Mbit/s (according to the different versions) |
| Max number of devices | 127 |
| Protocol | Serial |
USB is widely used and has the following advantages
- Applicable to a variety of peripherals, so there is no need to prepare different interfaces and protocols for different peripherals;
- Windows can auto-detect and auto-configure hot-swaps USB devices.
- Interface lines on the PC are very sparse and USB devices do not require users to specify ports. Therefore, USB excels in terms of usability and resource consumption.
- When connecting to a USB device, the maximum speed of the USB interface is up to 12 Mbit/s. Taking into account the status, control, and error information, the maximum theoretical speed can still reach 9.6Mbps, which is unachievable by other serial port protocols, and USB also supports low-speed transmission of 1.5Mbps.
- The low price of the USB interface chip also greatly promotes the development and application of USB devices.
Before the appearance of USB, the typical computer interface had a parallel port, serial port, mouse port, keyboard port, monitor port, and a variety of card interfaces, and these interfaces correspond to a variety of cables in terms of transmission speed, these interfaces have the problem of low speed. From a technological point of view, this design is prone to I/O contention, insufficient interrupts, and the need to design a new interface card for each new peripheral. Today’s computer outboards are in search of high speed and great versatility. The USB interface MEETS this requirement, and with its advantages of high speed, ease of use, and low cost, it quickly won the strong support of many PC manufacturers and semiconductor manufacturers. USB peripherals have become an inevitable trend.
USB system usage classification and system description
USB was originally designed for desktop computers, not mobile environments. The software system ensures future USB expansion by supporting multiple host controllers. USB is a cable bus that supports data transfer between a host computer and a variety of plug-and-play peripherals. A STANDARD PROTOCOL PER HOST ALLOWS MULTIPLE DEVICES TO SHARE USB BANDWIDTH AND THE BUS ALLOWS YOU TO ADD, CONFIGURE, USE AND REMOVE PERIPHERALS WHILE OTHER DEVICES AND HOSTS ARE RUNNING.
Description of USB system:
A USB system is mainly defined as three parts: USB interconnection, USB devices, and USB host.
USB connection refers to the connection and communication process between a USB device and a host, which mainly includes the following aspects:
- Bus topology: various connection modes between a USB device and host;
- Internal hierarchy: USB tasks are assigned to each hierarchy of the system according to performance overlay;
- Data flow mode: describes the flow mode of data in the system from the producer to the user through USB;
- USB scheduling: USB provides a shared connection. Available connections are scheduled to support synchronous data transfers and avoid the overhead of priority discrimination.
