Chapter 3 (1)

3.1 What is a bus? What are the characteristics of bus transmission? In order to reduce the load on the bus, what characteristics should the components on the bus have?

A bus is an information transmission bus that connects multiple components and is a shared transmission medium for each component.

At a certain time point, only one part can send information to the bus. Two or more parts can receive the same information from the bus at the same time.

The working rate of bus components should be highly consistent

 

How to classify the 3.2 bus? What is a system bus? The system bus is divided into several categories. What are their respective functions? Is it single or two-way? What are their relationships with machine characters, storage letters, and storage units?

Different connecting parts:

In-chip Bus: The bus inside the chip

System Bus: different transmission information: the two-way bits of the data bus are related to the machine Character length and storage character length.

One-way address bus is related to the number of storage units

Control bus bidirectional

Communication Bus: long-distance serial communication

Parallel Communication short distance

3.3 How many common bus structures are there? What is the impact of different bus structures on computer performance? Example?

A single bus structure is used in small computers, but it cannot solve the data transmission rate problem. The data transmission rates of different components are inconsistent.

Multi-bus structure

Dual-bus structure: separates low-speed I/O devices from a single bus to form a structure that separates the system bus from the I/O bus.

Used in large and medium-sized computer systems

Three-bus structure: main storage bus, DMA bus, I/O bus

Four-bus structure: add another high-speed bus and mount some high-speed I/O devices

 

3.4 why should I set up bus optimization control? There are several common centralized bus controls. What are their respective characteristics? Which of the following is the fastest way to meet each other? Which method is most sensitive to circuit faults?

Determine which part of the queue takes precedence over the bus.

Centralized bus control: chained Query

Advantages of the chained query method: bus arbitration can be achieved with only a few lines in a certain order of priority, and it is easy to expand the device. Disadvantages of the chain query method: It is very sensitive to circuit faults of the query chain. If the circuit related to the chain in the interface of the I device is faulty, devices after I cannot work. The query chain has a fixed priority. If a device with a higher priority receives frequent requests, the device with a lower priority may not be able to use the bus for a long time. Two wires

　　　　　　　　　　　　　　　　　　　　

Timed timer Query

When any device on the bus requires the use of the bus, the bus request is sent through the BR line. After receiving the request signal, the Central Arbitration server enables the counter to start counting when the BS line is "0". The count is sent to each device through a set of address lines. Each device interface has a device Address Identification circuit. When the Count value on the address line is the same as the device address on the request bus, the device sets the "1" BS line, after obtaining the right to use the bus, the Count query is aborted.

Each count can start from "0" or start from the center. If the priority of each device is the same as that of the chain query method from "0", the priority is fixed. If you start from the center, each device uses the same bus priority. The initial value of the counter can also be set by a program, which can easily change the priority, but this flexibility is at the cost of increasing the number of lines. Logn

Independent Request Method

Advantages of the independent request method: the response time is fast, and it takes less time to determine the priority response for the device, so you do not need to query the device by device. Second, when the priority control is flexible, it can be pre-fixed or changed through the program. It can also be used to block (prohibit) a request, does not respond to requests from invalid devices.

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Chapter 3 (1)