Bus (i)

There are two types of interconnection between the five parts of the computer system 1, using a separate line 2, each part connected to a set of public information transmission lines, called bus connections.

Early computer-centric computing, when IO exchange information, all need to pass the operator, so that the operator stop operation, affecting CPU efficiency.

At the same time, only one component is allowed to send information to the bus, while multiple parts receive the same information from the bus at the same time. A bus consisting of 16 transmission lines can transmit 16-bit binary code at the same time.

CPU-centric dual-bus:

CPU and IO Device Exchange data also need to pass CPU, so CPU efficiency or low.

Single bus:

In principle IO and memory transfer do not affect the CPU work, but when the time to occupy the bus, there will be a conflict, the need to set up a bus award.

Two-bus with main memory as the center:

The storage bus is fast and provides only the transfer between the CPU and main memory, and the IO device and main memory exchange data do not go through the CPU. Most computers now use this structure.

Bus classification: varies by connecting parts

1 on-chip bus: Inter-CPU, between registers, registers and Alu

2 system bus: The transmission of information between major components of CPU, main memory and IO device.

2.1 Data bus: bidirectional transmission, if the data bus width is 8 bits, instruction word length is 16, take instruction to access two times memory.

2.2 Address bus: The address of the data source, or the destination data on the IO device or main memory. Used to instruct the CPU to access the address, CPU output, unidirectional. The number of addresses of the address line is related to the storage unit, Address line 20, storage unit 2 20 times a

2.3 Control bus: Send control signal, for any control line is one-way. Sometimes the need to respond to the signal, but also can be seen as two-way.

3 Communication bus: Between computer systems, computer systems and other systems of communication between, divided into: Parallel communication, serial communication.

Parallel communication: Suitable for near-distance transmission, inversely proportional to transmission rate and distance

Serial communication: Suitable for long-distance transmission, inversely proportional to transmission rate and distance

Bus characteristics:

1 Mechanical properties: Characteristics in Mechanical connection mode

2 Electrical Characteristics: Transfer direction, active level

3 Features: transmission function for each line

4 time characteristics: In what time range is valid

Bus Performance Index:

1, Bus width: Data bus root number, 8 root, 16 root ...

2, Bus bandwidth: The number of bits that the bus transmits within a unit of time. Bus operating frequency 32MHZ, bus width 32 bits (4B), bus bandwidth of 33* (32/8) =132mbps

3, Clock synchronous/asynchronous: whether the data is synchronized with the clock.

4, Bus multiplexing: A signal line, time-sharing transmission two kinds of signals.

5, Number of data lines: data, control, address line sum

Bus (i)