Computer bus technology Basics

 

---- Any microprocessor must be connected to a certain number of components and peripheral devices. However, if each component and peripheral device are connected directly with a set of lines, the connection will be complicated and even difficult to implement. In order to simplify the design of hardware circuits and system structure, a group of lines are commonly used and configured to connect with components and peripheral devices with an appropriate interface circuit. This group of common connection lines is called bus. The bus structure is used to facilitate the expansion of components and equipment. In particular, the unified bus standard makes it easy to interconnect different devices. ---- In a microcomputer, bus generally includes internal BUS, system bus, and external bus. The internal BUS is the bus between peripheral chips and processors in the microcomputer and is used for first-level chip Interconnection. The system bus is the bus between the plug-in boards and system boards in the microcomputer, an external bus is the bus between a microcomputer and an external device. A Microcomputer acts as a device to exchange information and data with other devices, it is used for device-level interconnection. ---- In a broad sense, computer communication methods can be divided into parallel communication and serial communication. The corresponding communication bus is called parallel bus and serial bus. Parallel Communication is fast and real-time, but it is not suitable for small-sized products due to the large number of ports used. Although the serial communication speed is low, however, it is simpler, more convenient, and more flexible in microprocessing circuits with low Data Communication Throughput. Serial communication can be divided into asynchronous mode and synchronous mode. ---- With the development of micro-electronics and computer technology, bus technology is also constantly developing and improving, and the computer bus technology has a wide variety of features. Below we will only introduce the popular bus technologies in various types of micro-computers. I. Internal Bus 1. I2C bus (Inter-ic) bus was launched by Philips more than 10 years ago. It is a new type of bus standard widely used in the field of microelectronics communication control in recent years. It is a special form of synchronous communication. It has the advantages of few interface lines, simplified control mode, small encapsulation form, and high communication rate. In master-slave communication, multiple I2C bus devices can be connected to the I2C bus at the same time, and the communication objects can be identified by addresses. 2. SPI bus serial peripheral interface SPI (serial peripheral interface) bus technology is a synchronous serial interface launched by Motorola. The vast majority of MCU (microcontroller) manufactured by Motorola are equipped with SPI hardware interfaces, such as 68 series MCU. The SPI bus is a three-line synchronous bus. Because of its strong hardware functions, the software related to SPI is quite simple, so that the CPU has more time to process other transactions. 3. the SCI bus serial communication interface SCI (serial communication interface) was also launched by Motorola. It is a universal Asynchronous Communication Interface UART, And the asynchronous communication function of the MCS-51 is basically the same. Ii. System Bus 1. ISA bus (Industrial Standard Architecture) bus standard is a system bus standard established by IBM in 1984 to launch a PC/AT machine, so it is also called at bus. It is an extension of the XT bus to meet the requirements of the 8/16-bit data bus. It is widely used in the 80286-80486 era, so that there are still ISA bus slots in the Pentium. ISA bus has 98 pins. 2. EISA Bus is a bus standard jointly launched by 9 companies including Compaq in 1988. It uses a dual-layer socket based on the ISA bus. 98 signal lines are added to the 98 signal lines of the original ISA bus, that is, an EISA signal line is added between the two ISA signal lines. In practice, the eisa bus is fully compatible with the ISA bus signal. 3. VESA bus Video Electronics Standard Association is a local bus jointly launched by 60 accessory card manufacturers in 1992, referred to as VL (VESA Local Bus) bus. Its launch laid the foundation for the reform of the bus architecture of the microcomputer system. Considering the direct connection between the CPU and the main memory and the cache, this bus is usually called the CPU bus or the main bus. Other devices are connected to the CPU bus through the VL bus, therefore, the VL bus is called a local bus. It defines a 32-bit data line and can be extended to 64-bit through the expansion slot. It uses a 33 MHz clock frequency and has a maximum transmission rate of 132 Mb/s, which can work with the CPU. It is a high-speed and efficient local bus that supports ipvsx, ipvdx, 486sx, 486dx, and Pentium microprocessor. 4. the PCI bus PCI (Peripheral Component Interconnect) bus is one of the most popular bus and is a local bus launched by Intel. It defines a 32-Bit Data Bus and can be expanded to 64-bit. The size of the PCI bus motherboard slots is smaller than that of the original ISA bus slots. Its functions are greatly improved compared with VESA and ISA. It supports sudden read/write operations and the maximum transmission rate is 132 Mb/s, multiple groups of peripheral devices are supported at the same time. The PCI local bus is not compatible with the existing Isa, Eisa, and MCA (micro channel architecture) bus, but it is not subject to the processor and is developed based on the next-generation microprocessor such as Pentium. 5. the system buses listed above in Compact PCI are generally used in Commercial PCs. In computer system bus, there is another type of system bus designed to adapt to the industrial field environment, for example, std bus, VME bus, and PC/104 bus. This section only describes Compact PCI, one of the most popular bus for industrial computers. Compact PCI stands for "solid PCI", which is the first PCI system to adopt the Passive Bus baseboard structure today. It is an industrial assembly standard for PCI bus electrical and software standards and European cards, it is the latest industrial computer standard. Compact PCI is transformed from the original PCI bus. It uses the advantages of PCI to provide a high-performance core system that meets the requirements of industrial applications. At the same time, it also takes full advantage of traditional bus products, such as ISA, STD, Vme, or PC/104 to expand the system's I/O and other functions. 3. External Bus 1. RS-232-C bus RS-232-C is a serial physical interface standard developed by the American Association of Electronic Industry EIA (Electronic Industry Association. RS is the abbreviation of the English "Recommendation Standard". 232 indicates the ID number, and C indicates the number of modifications. RS-232-C bus standard has 25 signal lines, including a main channel and a secondary channel, in most cases the main channel, for general duplex communication, only a few signal lines can be achieved, such as a sending line, a receiving line, and a ground line. The RS-232-C standard sets the data transmission rate per second 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600 port. RS-232-C standards stipulate that the drive can have pf capacitive load, the communication distance will be limited by this capacitance, for example, when using a 150pf/M communication cable, the maximum communication distance is 15 m; if the electrical capacity of each meter cable is reduced, the communication distance can be increased. Another reason for short transmission distance is that the RS-232 is a single-ended signal transmission, there are common noise and can not suppress common mode interference and other problems, so it is generally used for communications within 20 m. 2. RS-485 bus widely adopts RS-485 serial bus standard when the communication distance is dozens of meters to kilometers. The RS-485 adopts balanced transmission and differential reception, so it has the ability to suppress common mode interference. In addition, the bus transceiver is highly sensitive and can detect voltage as low as 200mV. Therefore, the transmission signal can be recovered from kilometers away. RS-485 uses half duplex mode, at any time only a little in the sending State, therefore, the sending circuit must be controlled by the enabling signal. RS-485 for Multi-Point interconnection is very convenient, can save a lot of signal lines. The application RS-485 can be networked to form a distributed system that allows up to 32 drivers and 32 receivers in parallel. 3. IEEE-488 bus the above two types of external bus are serial bus, while IEEE-488 bus is parallel bus interface standard. IEEE-488 bus is used to connect systems, such as micro computer, digital voltmeter, digital display and other equipment and other instruments can be assembled with IEEE-488 bus. It transmits signals in two-way asynchronous mode in bit parallel and byte serial mode. The connection mode is bus mode, and the instrument and equipment are directly connected to the bus without intermediary units, however, up to 15 devices can be connected on the bus. The maximum transmission distance is 20 meters, the signal transmission speed is generally kb/s, and the maximum transmission speed is 1 Mb/s. 4. USB Bus Universal Serial Bus USB (Universal Serial Bus) it is a new interface standard jointly launched by seven world-renowned computer and communication companies, including Intel, Compaq, digital, IBM, Microsoft, NEC, and Northern Telecom. It is based on universal connection technology, achieving simple and fast connections to peripherals, so as to facilitate users, reduce costs, and expand the range of peripherals connected to PCs. It can provide power for peripherals, rather than a separate power supply system for general devices that use strings and ports. In addition, fast is one of the highlights of USB technology. The maximum transmission rate of USB is 100 times faster than the serial port and 10 times faster than the parallel port, and USB supports multimedia. From: http://blog.chinaunix.net/space.php? Uid = 1, 9105154