[assembly language 01] basic knowledge

1 Preface

1.1 Language development

1. course ： machine language → assembly language → High-level language
2. machine language ： People complete their tasks or projects in order to control computers , Can only write “0”、“ 1” Such a string of binary digits to control the computer , In fact, it is to control the high and low levels or open circuits of computer hardware , This language is machine language .
3. assembly language ： Machine language as a programming language , flexibility 、 Poor readability , In order to reduce the maladjustment brought by machine language to software engineers , People have upgraded and improved machine language ： Replace specific instructions with abbreviations that are easy to understand and remember .
4. High-level language ： To solve the portability of the program , We need to design one that does not depend on computer hardware , Programs that can run on different machines . This can avoid a lot of repeated programming process , Increase of efficiency , At the same time, this language is close to mathematical language or human natural language .

1.2 characteristic

1. advantage
   （1） You can easily read the memory status and hardware I/O Interface condition
   （2） The code is written because there are many less compilation Links , Can be executed accurately
   （3） As a low-level language , High scalability
2. shortcoming
   （1） Because the code is very monotonous , Special instruction characters are few , Therefore, the code is lengthy and difficult to write
   （2） Because the assembler still needs to call the memory to store data , It's easy to show up BUG, And it's not easy to debug
   （3） Even if you finish a program , Later maintenance also takes a lot of time .
   （4） Because of the particularity of the machine, there is a defect of poor code compatibility .

1.3 Why learn assembly language

Assembly language is a language that trains students to understand hardware resources , It is the basis for learning and understanding other high-level programming languages , Is the principle of computer composition 、 Interface and communication technology 、 Computer control technology and data acquisition are the leading courses of many professional courses , Is the necessary basic knowledge , Play a connecting role .

1.4 Learning focus

The research focuses on how to use the programming structure and instruction set of the hardware system to work effectively and flexibly .

2 Basic concepts of assembly language

The content of this chapter is mainly to understand the basic concepts , More knowledge points will be supplemented in the following places .

2.1 The composition of assembly language

1. Assembly instruction （ Mnemonics for machine codes ）： The core of assembly language is assembly instruction , It determines the characteristics of assembly language .
2. Pseudo instruction （ By compiler ）： There is no corresponding machine instruction , Its main function is to control the assembly process .
3. Other symbols （ Recognized by compiler ）： Add, subtract, multiply, divide, etc .

2.2 Assembly instruction

1. The main body of assembly language is assembly instruction , Assembly instructions are mnemonics for machine instructions .
2. The difference between assembly instructions and machine instructions lies in the representation of instructions , Assembly instruction is a writing format that is easy to memorize .
3. Example ：
   Operations to be implemented ： register BX To AX in
   Machine instructions ： 1000100111011000
   Assembly instruction ：MOV AX,BX
4. register ： Simply put, yes CPU A device that can store data in , One CPU There are multiple registers in .

2.3 Instructions and data

1. Instructions and data are applied concepts . On memory or disk , There is no difference between instructions and data , It's all binary information , Specifically as instructions or data , It is decided by the procedure .
2. Example ：
   binary data ：1000100111011000
   As data ：89D8H（H For hexadecimal ）
   Treat as instruction ：MOV AX,BX

2.4 Memory

2.4.1 Memory introduction

1. The function of memory ：
   CPU It's the core component of a computer ． It controls the operation of the whole computer and performs calculations , If you want a CPU Work , You have to give it instructions and data . Instructions and data are stored in memory , That's what we usually call memory
2. The status of memory ：
   At one PC The role of memory in the machine is second only to CPU. Out of memory , The best performance CPU Can't work .
3. Memory and disk ：
   Disk is different from memory , If the data or program on disk is not read into memory , You can't be CPU Use .

2.4.2 Storage unit

1. The memory is divided into several storage units , Each storage unit starts from 0 Start sequence number . Suppose a memory has 128 Storage unit , Then the number is from 0~127.
2. Each storage unit can store 1 Bytes Byte, namely 8 individual bit. Suppose a memory has 128 Storage unit , You can store 128B The content of .

2.4.3 classification

1. From the reading and writing properties, it can be divided into two categories ：
   （1） Ram （RAM）
   （2） read-only memory （ROM）
2. Classify from function and connection ：
   （1） Ram RAM
   （2） Equipped with BIOS Of ROM
   （3） On the interface card RAM

2.4.4 Logical connection of various memories

The logical connection diagram of various memories is as follows , Although all kinds of memory on the motherboard are physically independent devices , But they are the same in two ways ：
（1） And all CPU Bus connection of .
（2）CPU When reading or writing to them, the command of memory reading and writing is issued through the control line .

2.5 CPU Read and write to memory

1. CPU To read and write data , It has to be with external devices （ The standard way of saying is chip ） Interact with three types of information ：
   （1） Address of the storage unit （ Address information ）
   （2） Device selection , Read or write command （ Control information ）
   （3） Read or write data （ Data and information ）
2. that CPU By what will the address 、 Data and control information are transferred to the memory chip ？
   Computer can handle 、 All the information transmitted is electrical signals , Of course, electrical signals should be transmitted by wires . In the computer, there are special connections CPU And the wires of other chips , Commonly referred to as a bus .
3. understand CPU The process of reading and writing data into memory .

2.6 Bus

2.6.1 Bus Overview

1. Physically ： A collection of wires ;
2. Logically divided into ：
   （1） Address bus
   （2） data bus
   （3） Control bus
   

2.6.2 Address bus

1. CPU It is through the address bus to specify the storage unit .
2. How many different messages can be transmitted on the address bus ,CPU How many memory units can be addressed .
3. One CPU Yes N Root address bus , It can be said that CPU The address bus width of is N. In this way CPU At most, you can look for ２ Of N Next memory unit .

2.6.3 data bus

1. CPU Data transfer between memory and other devices is carried out through data bus .
2. The width of the data bus determines CPU And external data transmission speed ,8 The root data bus can 1 Secondary transmission 8 Bit data , namely 1 Bytes ,16 The root data bus can 1 Secondary transmission 16 Bit data , namely 2 Bytes .

2.6.4 Control bus

1. CPU The control of external devices is carried out through the control bus . Control information sent on the control bus .
2. Here, the control bus is a general term , A control bus is a collection of different control lines . How many control buses are there , Means CPU How many controls are provided for external devices . therefore , The width of the control bus determines CPU The ability to control external devices .

2.7 a main board

At every station PC In flight , There's a motherboard , There are core devices and some major devices on the motherboard . These devices go through the bus （ Address bus 、 data bus 、 Control bus ） Connected to a .

2.8 Interface card

In a computer system , All devices that can be programmed to control their operation , Must be subject to CPU The control of .CPU Cannot directly control external equipment , Like a display 、 Loudspeaker box 、 Printers, etc . Directly controlling these devices is the interface card inserted in the expansion slot .

2.9 Memory address space

1. Memory address space ： One CPU The width of the address line is 10, So you can address 1024 Memory units , this 1024 The memory units that can be found constitute this CPU Memory address space of .
2. Memory and memory address space ：CPU When operating each memory , Treat them as memory , They are generally regarded as a logical memory composed of several storage units , This logical memory is what we call memory address space .
   （1） All physical memory is regarded as a logical memory composed of several storage units ;
   （2） Each physical memory occupies an address segment in this logical memory , It's an address space ;
   （3）CPU Read and write data in this address space , In fact, it is to read and write data in the corresponding physical memory .
   

3 Summary

1. Assembly instructions are mnemonics for machine instructions , One to one correspondence with machine instructions .
2. Each of these CPU Each has its own assembly instruction set .
3. CPU Information that can be used directly is stored in memory .
4. There is no difference between instruction and data in memory , It's all binary information .
5. Storage units are numbered sequentially from zero .
6. A storage unit can store 8 individual bit （ Written as a unit “b”）, namely 8 Bit binary number , namely 1 Bytes .
7. every last CPU Chips have lots of pins , These pins are connected to the bus . It can also be said that , These pins lead to the bus . One CPU The width of three kinds of buses marks this CPU Different aspects of performance ：
   （1） The width of the address bus determines CPU The ability to address ;
   （2） The width of the data bus determines CPU The amount of data transferred at a time when data is transmitted with other devices ;
   （3） The width of the control bus determines CPU The ability to control other devices in the system .
8. Core thinking ： The final thing to run the program is CPU, When we use assembly programming , It must be from CPU Point of view .
   Yes CPU Speaking of , All memory units in the system are in a unified logical memory , Its capacity is limited by CPU Limitation of addressing capability . This logical memory is what we call the memory address space .

reference

1. 《 assembly language ( The first 3 edition ) 》 Wang Shuang , Main reference books and learning routes .
   Baidu cloud ：https://pan.baidu.com/s/1TE1Egc0ZmeJfLP5zvamo0Q
   Extraction code ：3y72
2. 《 Encyclopedia of assembly language 》
3. 《 Assembly language foundation 01》 Little turtle zero basic video course
4. 《 Assembly language foundation 02》 Little turtle zero basic video course
5. 《 Assembly language foundation 03》 Little turtle zero basic video course
6. 《 Assembly language foundation 04》 Little turtle zero basic video course
7. 《 Assembly language foundation 05》 Little turtle zero basic video course
8. 《 Assembly language learning notes 》