What Is a Memory Bus?

Bus (Bus) is a common communication trunk for transmitting information between various functional components of a computer. It is a transmission wiring harness composed of wires. According to the type of information transmitted by a computer, the computer's bus can be divided into a data bus, an address bus and a control bus , Used to transmit data, data address and control signals respectively. The bus is an internal structure. It is a common channel for the CPU, memory, input, and output devices to transmit information. The various components of the host are connected through the bus, and external devices are connected to the bus through corresponding interface circuits. system. In a computer system, a common path for transmitting information between various components is called a bus, and a microcomputer uses a bus structure to connect various functional components.

If the Mother Board is a city, then the bus is like a bus in the city. It can operate indefinitely according to a fixed driving route.

Because the bus is a set of signal lines connecting various components. Information is represented by signals on the signal lines, and how the operations are achieved can be agreed by agreeing on the order of the different signals. The characteristics of the bus are as follows

• (1) Physical characteristics:

  Physical characteristics, also known as mechanical characteristics, refer to some characteristics exhibited by the components on the bus when physically connected, such as the geometric size, shape, number of pins, and arrangement order of plugs and sockets.

• (2) Functional characteristics:
  Functional characteristics refer to the function of each signal line, such as the address bus used to represent address codes. The data bus is used to represent the transmitted data,

  The bus can be divided into five types according to functions and specifications:

  • Data Bus: Data that needs to be processed or stored between the CPU and RAM.

  • Address Bus: It is used to specify the address of data stored in RAM (Random Access Memory).

  • Control Bus: The signal from the microprocessor control unit is transmitted to the peripheral equipment.

  • Expansion Bus: A bus for data communication between external devices and the host computer, such as ISA bus and PCI bus.

  • Local Bus: An expansion bus that replaces higher-speed data transmission.

  External bus refers to the cable and connector system used to transmit the data and control signals specified by the I / O path technology. In addition, it also includes a bus termination resistor or circuit. This termination resistor is used to reduce signal reflection interference on the cable.

  The computer bus is a group of information transmission lines that can be shared in time-sharing for multiple components. It is used to connect multiple components and provide information exchange channels for them. A bus is not only a set of signal lines. In a broad sense, a bus is a set of transmission lines and related bus protocols.

  a. Motherboard bus

  In computer science and technology, people often describe the bus frequency with a speed expressed in MHz. There are many types of computer buses. The English name of the front-side bus is Front Side Bus, which is usually represented by FSB. It connects the CPU to

  1. of the bus

  Motherboard

  One operation process of the bus is to complete the transmission of information between the two modules. The master module and the slave module start the operation process. Only one master module can occupy the bus at any one time.

  Operation steps of the bus:

  The master module applies for bus control, and the bus controller decides.

  Operation steps of the bus:

  After the master module gets the bus control right, it addresses the slave module, and after the slave module confirms, it transmits data.

  Why develop a bus standard?

  Convenient for the expansion of machines and the addition of new equipment. With the bus standard, different manufacturers can produce chips, modules and complete machines with different functions according to the same standards and specifications. Users can choose based on functional requirements to Modules and devices of the same kind of bus standard can even design their own special modules and devices with special functions according to the standards to form their own application system. In this way, products at all levels such as chip level, module level, and equipment level are compatible and interchangeable, so that the maintainability and expandability of the entire computer system can be fully guaranteed.

  Technical specifications of the bus standard?

  Mechanical structure specifications: The module size, bus plug, bus connector, and installation size are all uniformly specified.
  Functional specifications: Each signal line (name of the pin), function, and working process of the bus must have uniform regulations.
  Electrical specifications: effective level of each signal line of the bus, dynamic conversion time, load capacity, etc.

  Which bus is standard?

  The processor-main memory bus on the motherboard is often a special dedicated bus, and the I / O bus and backplane bus used to connect various I / O modules are usually interoperable in different computers. In fact, backplane buses and I / O buses are usually standard buses that can be used by many different computers made by different companies.

  Bus Standard-ISA

  The ISA (Industrial Standard Architecture) bus is a system bus standard established by IBM in 1984 for the introduction of PC / AT machines. So it is also called AT bus.

  main feature:

  (1) Support 64KI / O address space, 16M main memory address space addressing, support 15 hard interrupts, 7 DMA channels.

  (2) is a simple multi-master bus. In addition to the CPU, DMA controllers, DRAM refresh controllers, and intelligent interface control cards with processors can all become bus masters.

  (3) Supports 8 types of bus transactions: memory read, memory write, I / O read, I / O write, interrupt response, DMA response, memory refresh, and bus arbitration.

  It has a clock frequency of 8MHz and a total of 98 signal lines. The data line is separated from the address line. The width of the data line is 16 bits, and 8-bit or 16-bit data can be transmitted, so the maximum data transfer rate is 16MB / s.

  Bus Standard-EISA

  EISA (ExtendedIndustrialStanderdArchitecture) bus is an open bus standard extended on the basis of ISA bus. Support multi-bus master control and burst transmission mode.

  The clock frequency is 8.33MHz. There are 198 signal lines in total, and 100 lines are expanded on the basis of 98 lines of the original ISA bus, which is completely compatible with the original ISA bus. With separate data and address lines. The data line width is 32 bits, with 8-bit, 16-bit, and 32-bit data transmission capabilities, so the maximum data transfer rate is 33MB / s. The width of the address line is 32 bits, so the addressability is up to 232. That is, the main control devices such as the CPU or the DMA controller can access the main memory address space in the 4G range.

  Bus Standard-PCI

  PCI (PeripheralComponentInterconnect) bus

  It is a high-performance 32-bit local bus. It was proposed by Intel Corporation at the end of 1991, and later joined with more than 100 major manufacturers in the PC industry such as IBM and DEC. In 1992, it established the PCI Group, called PCISIG, to coordinate and promote the PCI standard.

  The I / O interface for high-speed peripherals is connected to the host. Using its own 33MHz bus frequency, the data line width is 32 bits, which can be expanded to 64 bits, so the data transmission rate can reach 132MB / s 264MB / s.

  Fast speed, support unlimited burst transmission mode, support concurrent work (PCI bridge provides data buffering, and makes the bus independent of the CPU), can be connected to other system buses (such as: ISA, EISA or MCA) on the motherboard, in the system High-speed devices are connected to the PCI bus, while low-speed devices are still supported by these low-speed I / O buses such as ISA and EISA. Supports microprocessor-based configurations and can be used in uniprocessor systems as well as multiprocessor systems.

  Main advantages of using a bus structure

  1. The memory-oriented dual-bus structure has high information transfer efficiency, which is its main advantage. However, when both the CPU and I / O interfaces access the memory, conflicts still occur.

  2. The CPU is connected to the high-speed local memory and local I / O interface through a local bus with a high transfer rate. The slower global memory and global I / O interface are connected to the slower global bus, thus taking into account both high-speed equipment and Speed equipment so that they do not involve each other.

  3. Simplified hardware design. It is easy to adopt a modular structure design method, and the bus-oriented microcomputer design is only required to make the CPU

  Any microprocessor must be connected to a certain number of components and peripherals, but if each component and each peripheral

  1.	intermediate distribution bus Intermediate distribution bus
  2.	VESA local bus (VL-bus) VESA Local bus
  3.	analysis, bus bounce Bus Jitter Analysis
  4.	analog summing bus Analog addition bus
  5.	architecture, micro-channel bus (MCA) Micro-channel bus (architecture) structure
  6.	arbitration bus Arbitration bus
  7.	arbiter, bus Bus arbiter
  8.	backplane bus Scaffold bus
  9.	back-off, bus Bus exit
  10.	base bus Base Bus
  11.	bus-timing emulation Bus timing simulation
  12.	bus-intensive Bus-intensive
  13.	bus-control unit Bus control unit
  14.	bus, utility Utility bus
  15.	bus, summing Addition bus
  16.	bus, realtime system integration (RTSIBus) Real-time system bus
  17.	bus, peripheral interface Peripheral interface bus
  18.	bus, multisystem extension interface (MXIbus) Multi-system extension interface bus
  19.	bus, multidrop parallel Branch parallel bus
  20.	bus, micro-channel Microchannel bus