Process technology materials
USB is the abbreviation of Universal Series Bus (Universal Serial Bus), which is a serial communication protocol (sereal protocol), which is responsible for the establishment of the physical layer and link layer. It can support slow data transmission (such as mouse, keyboard, game joystick, etc.) and fast digital compression of audio and video information. The ordinary USB2.0 version has two pairs of wires below, which are used to transmit data and provide the power cord required by the interface device. The standards before version 2.0 defined the speeds as 12Mbps (Full Speed) and 1.5Mbps (Low Speed) ) High-speed and low-speed cables, each with the Type A connector on the upstream Host side and the Type B connector on the downstream Device side to form a USB cable assembly (Cable Assembly). Through the USB hub (Hub) and the root hub (Root Hub) inside the computer, a star network can be formed, and as the number of hubs increases, the scale of the network increases accordingly. Therefore, it replaces the traditional various external ports with a universal connector, such as serial port, game interface and parallel port, etc. USB and can allow up to 127 interface devices to be serially connected to an external USB port It doesn't have to be like the current serial port or parallel port, one port can only be connected to one interface device. As shown in the figure, to put it simply, it is to simplify the connection between the external interface device and the host, and use a transmission line to connect various interface devices in parallel to solve the plight of a large number of lines behind the host. Moreover, various interface devices can be installed at any time without restarting or installing. In order to enable the end user to simplify the process of connecting and planning the computer peripheral equipment.
USB is a connection standard. It can directly connect the interface device to the computer without reconfiguring the system, providing a broader future for plug-and-play (PnP, hot-swapping) and increasing the user's use. Convenient and fast. At present, USB can reach the USB4 stage, up to 40Gbps (High speed) high-speed transmission target, has exceeded the speed set by the IEEE1394-1995 specifications, even if the USB still has some problems to be solved, but the USB that takes up the price and technical advantages will become a PC The mainstream of bus standards is already an inevitable trend.
Brief description of the main features of USB
USB provides a low-cost solution for connecting peripheral devices, and can connect up to 127 devices at a time.
l Hot swap and Plug & Play functions:
The USB automatic detection device is connected, and the software will automatically plan it for immediate use. No user intervention is required during this process.
l Cable power supply:
USB supports multiple transfer rates, which can be divided into low speed (Low Speed) 1.5Mb / s and high speed (Full Speed) 12Mb / s. Another version 2.0 USB transfer rate is 480Mb / s, version 3.0 USB transfer rate is 4980Mb / s; version 3.1 USB transfer rate is 10G / Mbps; the USB4 transfer rate that will be commercialized at the end of the year is even more terrifying 40G / Mbps; version of Among them, the former makes the use of low-speed / low-cost devices possible. This is because the cable can be designed so that it does not require shielding and the price is reduced. Peripheral devices can be directly powered by cables. The latter can provide 5.0VDC power. Depending on the hub connector port, the current range of USB2.0 series and below is 100mA-500mA; and USB 3.0 provides 5V / 0.9A power supply. But people still hope for a stronger power supply capability, so USB 3.1 (SuperSpeed +) has increased the maximum allowable standard of power supply to 20V / 5A, power supply 100W.
l Eliminate system resource requirements:
Unlike ISA, EISA, and PCI devices, USB devices do not require memory or input / output address space (DMA) and IRQ lines.
l Error detection and recovery:
USB transactions include an error detection mechanism to ensure the correct transfer of data. When an error occurs, the transaction will be retried.
l Save energy:
If there is no action after 3ms bus, the USB device will automatically enter the power saving state. At this time, the current consumed by the device does not exceed 500uA.
l Support four kinds of transmission:
USB defines four transmission modes to support the needs of various devices. These four forms include (huge volume, real-time, interrupt and control transmission).
ISA: industry standard architecture
EISA: Extended industry standard architecture
PCI: Peripheral Component Interconnect
DMA: Direct Memory Access
IRQ: Interrupt Request