【 Weak current College 】 bus small known common sense 】

----Any microprocessor with a certain number of parts and peripherals connected, but if you put all parts and every kind of peripheral devices are represented by a set of lines and CPU direct connection, the connection will be complicated, even difficult to achieve. In order to simplify the hardware circuit design, simplified system architecture, a common set of lines, the configuration to an appropriate interface circuit, and the various components and peripheral devices, this group share the connection lines is called the bus. A bus structure facilitates the expansion of the parts and equipment, in particular to develop a unified standard you can easily make the bus between devices for interconnection.

----Computer bus usually have internal bus, system bus and the external bus. Internal bus is a microcomputer internal peripheral chip and processor bus for chip-level interconnection; whereas the system bus is the Board in the microcomputer and system board between bus for Board level interconnection; external bus is a computer and an external device, the computer between bus as a device through the bus, and other devices for information and data exchange, it is used to interconnect device level.

----Other, broadly speaking, the computer communication methods can be divided into parallel communication and serial communication, the communication bus is called parallel bus and serial bus. Parallel communication speed, real-time performance is good, but because of the use of line, not suitable for the miniaturization of products; whereas the serial communication speed is low, but not in data traffic throughput is a lot of micro-processing circuit, it is much more simple, convenient and flexible. Serial communication in General can be divided into asynchronous mode and synchronization mode. ----As microelectronics and computer technology, bus technology is constantly developing and improving, and making your computer bus technology range. The following is only for PC in all kinds of bus is currently more popular bus technology respectively.

First, the internal bus

----1.I2C bus----I2C (Inter-IC) bus 10 years ago by the Philips company launched in recent years in the field of microelectronics communication control wide adoption of a new type of bus standards. It is synchronous communication a special form, have less control interface line simplification, the device package form small, communication rate is higher merit. In master-slave communication, you can have multiple devices at the same time receiving the I2C bus I2C bus, through the address to identify the communication object.

----2.SPI bus-serial peripheral interface SPI (serialperipheralinterface) bus technology is the Motorola company launched a synchronous serial interface. Motorola company most MCU (microcontroller) are equipped with SPI interface, such as 68 series MCU. SPI-bus is a three-line synchronization bus, because of its hardware features a very strong, and SPI related software is quite simple, so that CPU and more time working on other services.

----3.SCI bus-serial communication interface SCI (serialcommunicationinterface) was launched by Motorola company. It is a generic asynchronous communication interface UART, and asynchronous communication function MCS-51 basically the same.

Second, the system bus

----1.ISA bus-ISA (industrialstandardarchitecture) bus standard is the IBM PC in 1984 to launch and establish AT machine/system bus standard, also known AT bus. It is an extension of the XT bus to accommodate 8/16 bit data bus. Its application in the era of 80286-80486 is extensive, so that now the Pentium machines also have ISA bus slot. ISA bus 98 only pin.

----2.EISA Bus----EISA bus is 1988 by Compaq, 9 companies joint launch of bus standards. It is in the ISA bus, based on the use of double-outlet, in the original ISA bus 98 signal cable on an additional 98 signal lines, that is, two ISAsignal lines between an EISA signal cable. In practical, EISA bus is fully compatible with ISA bus signals.

----3.VESA bus--VESA (videoelectronicsstandardassociation) bus is 1992 by 60 annex card manufacturer United Launch of a local bus, known as VL (VESAlocalbus) bus. Its launch is a computer system bus architecture has laid the Foundation for innovation. The bus system considering the CPU and main memory and the Cache is usually directly connected to this part of the bus called CPU bus or bus and other equipment by VL-bus and CPU bus is connected, the VL bus called the local bus. It defines the 32-bit data line, and can be extended through the expansion slots to the 64-bit, use 33MHz clock frequency, the maximum transfer rate of up to 132MB/s that can be synchronized with the CPU. Is a high-speed, efficient local bus to support 386SX, 386DX, 486SX, 486DX and Pentium microprocessor.

----4.PCI bus-PCI (peripheralcomponentinterconnect) bus is currently one of the most popular bus, it is by Intel Corporation launched a local bus. It defines the 32-bit data bus, and scalable for 64-bit. PCI motherboard socket volume ratio of the original ISA bus slot still small, its function is VESA, ISA has greatly improved support for sudden reads and writes, the maximum transfer rate of up to 132MB/s, while supporting more than one set of peripherals. PCI local bus is not compatible with the existing ISA, EISA, MCA (microchannelarchitecture) bus, but it is not subject to the processor that is based on the Pentium, a new generation of microprocessors and development of the bus.

----5.CompactPCI----the above cited several system bus is generally used for commercial PC machine, in a computer system bus, there is another class in order to adapt the industrial scene environment system bus, such as STD bus, VME, PC/104 bus, etc. Here only describes current industry one of the most popular bus of the computer — CompactPCI. ----CompactPCI mean "solid PCI", is the first with passive bus floor structure of PCI system, is a PCI bus electrical and software standards and European card of industrial packaging standard, is the latest of an industry-standard computers. CompactPCI is originally based on the transformation of the PCI bus, it utilizes the advantages of PCI, meet the requirements of industrial and environmental applications of high-performance core system, while also considering the full use of the traditional bus products, such as ISA, STD, VME or PC/104 expansion System i/o and other features.

III. external bus

----1.RS-232-C bus----RS-232-C is United States electronic industries Association of EIA (ElectronicIndustryAssociation) developed a serial physical interface standard. RS is in English "recommendation", 232-identification number, c for change frequently. RS-232-C bus standard equipped with 25 of signal lines, including a main channel and an auxiliary channel, in most cases, mainly using the main channel, duplex communication in General, you only need a few signal lines can be achieved, such as a send line, one receive line and a ground wire. RS-232-C standards for data transmission rate is per second, 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 Porter. RS-232-C standard requirements drive allows 2500pF of capacitive load, communication distance will be affected by this capacitance limits, for example, the use of communication 150pF/m cable, maximum communication distance is 15m; if every metre cable capacity decreases, the communication distance can be increased. Transmission distance short another reason is that in the case of single-ended signal transmission RS-232, there is a total and noise and common mode interference cannot be suppressed, so typically used within 20m communications.

----2.RS-485 bus-in requirement communications distance of dozens of meters to km, widely adopted RS-485 serial bus standards. RS-485 adopts balanced send and receive, and therefore have differential inhibition of common mode interference. Coupled with the bus transceiver with high sensitivity, detection of low-voltage 200mV, transmitting signals can be restored at km away. RS-485 using half-duplex working mode, any time you can only have one point in the sending State, therefore, send circuit shall be determined by the signal control. RS-485 for multipoint interconnect handy, you can save a lot of signal lines. Application constitutes interconnection RS-485 can distributed system, which allows up to 32 drives in parallel, and 32 single sink.

----3.IEEE-488 bus----the above two external bus is a serial bus, a bus is IEEE-488 parallel bus interface standard. IEEE-488 bus used to connect to the system, such as micro-computers, digital voltmeters, digital display equipment and other instruments and meters are available IEEE-488 bus together. It follow bit parallel, byte serial bidirectional transmission signal asynchronously, connections to bus, instrument and equipment directly parallel to the bus without intermediate unit, but the bus up to 15 devices can be connected. Maximum transmission distance of 20 meters, signal transmission speed is 500 KB/s maximum transfer speed of 1 MB/s.

----4.USB bus---universal serial bus USB (universalserialbus) is made by Intel, Compaq, Digital, IBM, Microsoft, NEC, NorthernTelecom, 7 of the world's leading computer and communications companies jointly launched a new interface standards. It is based on the generic connection technology, the realization of a simple and quick connect peripherals, achieve the convenience of users, reduce costs, expand the range of PC peripherals. It provides power for peripherals, and unlike ordinary using series and parallel port devices require a separate power supply system. In addition, fast is the outstanding characteristic of USB technology, USB, one of the highest rate up to 12Mbps 100 times faster than a serial port, parallel port, nearly 10 times faster, but also to support multimedia USB.