Past and Present
USB, the full name is Universal Serial Bus, which was born in 1974, Double Eleven>: In that era, the PC era had arrived, and the Internet era had not yet arrived. Personal computers were surging in the world, and various devices were springing up like mushrooms after a rain. , various interfaces are also strange, and various serial ports and parallel ports are popular. In order to unify PC interfaces and simplify product design, USB was born. With its impeccable design and excellent performance, it quickly occupied the PC interface market and became the most widely used interface on PCs.
character
Just by looking at its name, we can know the characteristics of USB, which are: open (Universal), simple (Serial), tolerant (Bus), and thoughtful (the protocol is complex).
- Open: The interface rules are completely open. Any device manufacturer who wants to use USB as a communication interface can perfectly access the system by following the specifications. Whether you have a simple mouse, keyboard, game joystick device, etc., or a complex one printers, mobile phones, cameras, etc., as long as you comply with USB specifications, USB will treat you equally, so USB is open.
- Simplicity: USB hardware design is very simple. From USB1.0 to USB2.0, there are only four cables, two for power supply and two for communication. The signals passing through USB are all serial and half-duplex. The signals on it are very "simple". They are all analog signals (differential signals) representing 0 and 1. Therefore, USB is simple.
- Tolerance: USB is a bus type. A USB bus has only one Host (host controller, equivalent to the brain of USB), several USB HUBs (used to expand the USB interface), and USB devices are mounted on the HUB. In theory, one The USB bus can connect 127 devices (the USB address is 7bit). USB devices are like countless small rivers. Through the "bus" of the big river, they finally converge to the USB host controller. This "ocean", as the saying goes, is full of rivers, so USB is inclusive.
- Thoughtful: The hardware model of the USB interface is simple, but the idea is indeed very profound. Because of the diversity of USB devices, sophisticated strategies must be used to effectively manage various USB devices. The complexity of USB lies in this. Its communication protocol is very complex. Device enumeration, control, data communication, etc. are all implemented through software protocols. This is what people love and hate about USB. Its hardware interface is very simple and the hardware cost is low. However, the communication protocol is very complex and the software cost is high.