What are the classifications of buses?

Bus can be divided into five types according to functions and specifications: Data Bus, Address Bus, Control Bus, Expansion Bus, and Local Bus (Local Bus).

Bus (Bus) is a public communication trunk for transmitting information between various functional components of the computer. It is a transmission harness composed of wires. According to the transmission of the computer According to the type of information, the computer bus can be divided into data bus, address bus and control bus, which are used to transmit data, data address and control signals respectively.

The bus is an internal structure. It is a common channel for CPU, memory, input and output devices to transmit information. The various components of the host are connected through the bus, and the external devices are connected to each other through the corresponding interface circuits. Buses are connected to form a computer hardware system.

In a computer system, the common channel for transmitting information between various components is called a bus. Microcomputers use a bus structure to connect various functional components.

Bus can be divided into five types according to their functions and specifications:

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

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

• Control Bus: Transmits signals from the microprocessor control unit (Control Unit) to peripheral devices.

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

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

The data bus DB (Data Bus), address bus AB (Address Bus) and control bus CB (Control Bus) are also collectively referred to as the system bus, which is commonly known as bus.

Bus characteristics

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

(1) Physical characteristics: Physical characteristics are also called mechanical characteristics, which refer to some characteristics of the components on the bus when they are physically connected, such as the geometric size, shape, and pins of plugs and sockets. Number and arrangement order, etc.

(2) Functional characteristics: Functional characteristics refer to the function of each signal line, such as the address bus used to represent the address code. The data bus is used to represent transmitted data, and the control bus represents the commands, status, etc. operated on the bus.

(3) Electrical characteristics: Electrical characteristics refer to the signal direction on each signal line and the effective level range of the signal. Usually, the signal sent by the main device (such as CPU) is called the output signal (OUT), the signal sent to the host device is called the input signal (IN). Usually data signals and address signals define high level as logic 1 and low level as logic 0. There is no conventional convention for control signals. For example, WE means low level is valid and Ready means high level is valid. There are no unified regulations on the level ranges of high and low levels of different buses, and they are usually consistent with TTL.

(4) Time characteristics: Time characteristics, also known as logic characteristics, refer to when the signal on each signal line is valid during the bus operation. Through this agreement on the timing relationship of the signal validity, the bus is ensured correct operation. In order to improve the scalability of computers and the versatility of components and equipment, in addition to the on-chip bus, each component or equipment is connected to the bus in a standardized form, and information transmission on the bus is implemented in a standardized manner. These standardized connection forms and operation methods of the bus are collectively called bus standards. Such as ISA, PCI, USB bus standards, etc. Correspondingly, buses using these standards are ISA bus, PCI bus, USB bus, etc.

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