Computer Motherboard bus technology basics

Any of a microprocessor to be with the number of components and peripheral devices to connect, but if each of the various components and peripherals
Prepared respectively by a group of lines directly connected with the CPU, then the connection will be complex, even difficult to achieve.
In order to simplify
Hardware circuit design, simplify the system structure, a set of commonly used lines, configure the appropriate interface circuit, with various components and peripherals
Preparation of connections, this group of lines is called sharing the connection bus. Bus structure used to facilitate the expansion of parts and equipment, in particular, to develop
A unified bus standard is likely to achieve the interconnection of different devices.
---- Microcomputer generally have internal bus in the bus, system bus and external bus. Internal bus is the internal microcomputer chip and the peripheral
Between the processor bus for chip-level interconnect; while the system bus is a computer in each plug-in board and system board between the total
Line for the plug-in board-level interconnect; external bus is a computer and external devices bus, microcomputer as a device,
Through the bus and other devices for information and data exchange, it is used for device-level interconnect.
---- In addition, broadly speaking, the computer means of communication can be divided into parallel communication and serial communication, and the corresponding communication bus is
Referred to as a parallel bus and serial bus. Fast parallel communication, real-time good, but because they are occupying the mouth lines and more unfit for a small
Chemical products; and serial communication rate was low, but the data communications throughput is not large in the micro-processing circuit is even more simple
Easy, convenient and flexible. Serial communication in general can be divided into asynchronous mode and synchronous mode.
---- With the microelectronics and computer technology, bus technology is continually developing and improving, leaving the total computer
Line technology varies widely, with different features. The following types of bus-only computer currently popular bus technology were to be referred
1, the internal bus
---- 1. I2C-bus
---- I2C (Inter-IC) bus more than 10 years ago by the Philips company introduced in recent years, a broad field of communication control in microelectronics
Adopted a new type of bus standard. It is a special form of synchronous communication with interface cable less control method simplified,
The device package is small, the advantages of a higher communication speed. In the master-slave communication, you can have multiple I2C devices on the bus at the same time received a
I2C bus, through the address to identify the communication objects.
---- 2. SPI Bus
---- Serial peripheral interface SPI (serial peripheral interface) bus technology is Motorola has introduced a
Synchronous serial interface. Motorola produced the vast majority of MCU (micro-controllers) are equipped with SPI hardware interface, such as the
68 Series MCU. SPI bus is a three-wire synchronous bus, because of its strong hardware functions, therefore, with the SPI-related soft -
Piece is quite simple, so that more CPU time to handle other matters.
---- 3. SCI Bus
---- Serial communication interface SCI (serial communication interface) is introduced by the Motorola Corporation. It is a
Kinds of universal asynchronous communication interface UART, and MCS-51 of the asynchronous communication function basically the same.
2, system bus
---- 1. ISA Bus
---- ISA (industrial standard architecture) bus standard is the IBM Corporation in 1984 for the introduction of PC / AT machine built
Li's system bus standard, also called the AT bus. It is the XT expansion bus to accommodate the 8 / 16 bit data bus to be
Demand. 80286-80486 times it is widely used, so that now the Pentium machine also retain ISA bus slot.
ISA bus has 98 pins.
---- 2. EISA bus
---- EISA bus is in 1988 by Compaq and other nine co-launched bus standard. It is the base ISA bus
That basis the use of double-socket, in the original ISA bus 98 signal lines were added to 98 signal lines, that is, two
ISA added between the signal lines of an EISA signal line. In the utility of, EISA bus is fully compatible with ISA bus signals.
---- 3. VESA Bus
---- VESA (video electronics standard association) bus is the annex in 1992 by the 60 card manufacturer Joint
Launch of a local bus, referred to as the VL (VESA local bus) bus. It is the introduction of the microcomputer system bus architecture
Laid the foundation for innovation. The bus system taking into account the CPU and main memory and the Cache directly connected to this part is usually the total
Line known as the CPU bus or host bus, other equipment through the VL bus and CPU bus connected to, it is known as the VL-bus
Local bus. It defines a 32-bit data lines, and can be extended to a 64-bit expansion slot, use the 33MHz clock frequency,
Maximum transfer rate up to 132MB / s, can be synchronized with the CPU work. Is a high-speed, efficient local bus to support 386SX,
386DX, 486SX, 486DX and Pentium microprocessors.
---- 4. PCI Bus
---- PCI (peripheral component interconnect) bus is one of the most popular bus, which is recognized by the Intel
Division launched a local bus. It defines a 32-bit data bus, and can be extended to 64 bits. PCI-bus board slots
Volume than the original ISA bus slot is still small, its function than the VESA, ISA has greatly improved, support for burst read and write operations, the most
Large transfer rate of up to 132MB / s, can simultaneously support multiple peripherals. PCI Local Bus can not be compatible with existing ISA,
EISA, MCA (micro channel architecture) bus, but it is not subject to the processor is based on the Pentium and other new one
Generation of microprocessors and the development of the bus.
---- 5. Compact PCI
---- Several listed above system bus is generally used for commercial PC machine, in a computer system bus, there is another
Major categories to meet the industrial field environments designed system bus, such as the STD bus, VME bus, PC/104 bus, and so on.
Here is only on current industrial computer, one of the most popular bus - Compact PCI.
---- Compact PCI means "a solid PCI", is today the first use of a passive backplane architecture of the PCI bus system,
Is a PCI bus, electrical and software standards for European Union, the industrial assembly-type card standard, today's the latest of a standard industrial computer
Quasi. Compact PCI is a PCI bus based on the transformation of the original from which uses the advantages of PCI to provide to meet the industrial ring
Applications require high-performance throughout the core system, also taking full use of traditional bus products, such as ISA, STD, VME
Or PC/104 to expand the system I / O and other functions.
3, external bus
---- 1. RS-232-C-bus
---- RS-232-C is the American Electronics Industry Association EIA (Electronic Industry Association) developed a serial object
Li interface standard. RS is in English "recommended standard" abbreviation, 232 for the identification number, C indicated that the number of changes. RS-232-C
Bus standard equipped with 25 signal lines, including a main channel and an auxiliary channel, in most cases, mainly in the main pass
Road, for the general duplex communication, only a few signal lines can be achieved, such as a transmission line, a receiving line and a ground wire.
RS-232-C standard specifies the data transfer rate of 50,75 per second, 100,150,300,600,1200,2400,4800,
9600,19200 Porter. RS-232-C standard requirements, the drive allows 2500pF capacitive load, communication distance will be subject to
This capacitance limits, for example, use of 150pF / m communication cable, the maximum communication distance of 15m; if the electrical cable per meter
Capacity decreases, communication range can be increased. Another reason for the short transmission distance is the RS-232 is a single-ended signal transmission, there are a total of
To suppress common mode noise and can not interfere with issues such as are generally used for communication within 20m.
---- 2. RS-485 bus
---- In the required communication distance of tens of meters to the previous 1000 meters, the widely used RS-485 serial bus standard. RS-485 uses flat
Value transmission and differential receive and therefore have the ability to suppress common mode interference. Coupled with bus transceiver with high sensitivity, can detect
Voltage as low as 200mV, so the signal can be transmitted outside of 1000 meters to be restored. RS-485 half-duplex mode,
There can be only one point at any time to send state, therefore, to send the circuit to be controlled by the enable signal. RS-485 for
Multi-point interconnection is very convenient, you can dispense with a number of signal lines. Application of RS-485 can constitute a network distributed systems, Yun
Xu maximum parallel 32 drivers and 32 receivers.
---- 3. IEEE-488 bus
---- Of the two external bus is a serial bus, while the IEEE-488 bus is a parallel bus interface standard. IEEE-488 bus
Is used to connect systems, such as micro-computers, digital voltmeter, digital displays and other equipment and other instruments are available
IEEE-488 bus assembly together. It is in bit parallel, byte serial bi-directional asynchronous transfer mode signal, the total connection
-Line, instruments and equipment in parallel on the bus directly without an intermediary unit, but the bus can connect up to 15 devices. Most
Large transmission distance of 20 meters, the signal transmission speed is usually 500KB / s, maximum transmission speed of 1MB / s.
---- 4. USB bus
--- Universal Serial Bus USB (universal serial bus) from Intel, Compaq, Digital, IBM, Microsoft,
NEC, Northern Telecom and other seven world-famous computer and communications companies jointly launched a new interface standard.
It is based on universal connectivity technology to realize a simple quick connect peripherals to achieve user-friendly, reduce costs, extended PC connectivity
The scope of the purpose of peripherals. It can provide power for the peripherals, rather than the use of ordinary string, parallel port devices require a separate supply
Power system. In addition, the fast is one of the salient features of USB technology, USB's maximum transfer rate of up to 12Mbps over serial port
100 times faster, nearly 10 times faster than the parallel port, but USB can support multimedia.