---
tags : 微算機與組合語言
---
###### 國立臺北大學資工系江宥旻
Assembly Language Programming
===
Software：The microcomputer program
---
Hierarchy of Programming Language
+ High Level Language

    int a = 0, b = 0;
    a = 2;
    b = 5;
    a = a * a + 3 * b + 6;
    printf("The Integer: %d", a);

+ Low Level Language (Assembly Language)

    MOV ax, 2
    MOV cx, ax
    MOV bx, 5
    mul ax, cx
    add ax, bx

+ Machine Language

    1001000100011110
    0111001010010101
    1100110101110101
    1110001111011010
    0101110101010101

+ CPU Execution
+ Fetch Instruction
+ Decoding
+ Retrieve Data
+ Execution
+ Write Back

Native language is machine language
+ A program written in machine language is often called machine code
+ Is encoded using 0, 1
+ An instruction can be divided into two parts
+ Operation code (opcode)運算子
+ Operands運算元
+ Each opcode is assigned a unique letter combination called a `mnemonic(助憶碼)`
+ MOV AX, BX
+ Move bx register to ax register
+ Physically cpu copies the value of BX into AX
+ BX is source operand and AX is destination operand
---
Simple program that can be translated into machine code using MASM 6.0

MASM (將組合語言轉成機器碼)
+ Macro Assembler
+ Translating mnemonic code into machine code (object code)

;*****************
;*   SIMPLE.ASM
;*****************
.MODEL small
.DATA
     CR EQU 0DH                   ;EQU等於用來定義常數DB define byte
     LF EQU 0AH
     ONE DB 01h
     MESSAGE DB 'smile’, CR, LF, '$'
.CODE
start:  
     MOV ax, @data               ;DS 移到資料區開始地
     MOV ds, ax
     MOV ah, 02h
     MOV dl, ONE
     int 21h
     MOV ah,09h
     MOV dx,OFFSET MESSAGE      ;DX 移到字串的位址
     int 21h
     MOV ah,4ch
     int 21h
.STACK
END start

:::info
一個程式會有三個區
+ .DATA 資料區
+ .CODE 程式區
+ .STACK 堆疊區
:::
> 組譯程式把組合語言轉換成機器碼
> OD、OA(CR、LF)：carriage return and line feed (游標移到最前並換行)


[INT 21H 指令說明及使用方法](https://www.796t.com/content/1548310330.html)
int 21h是一種中斷程式(interrupt)是OS提供給APP使用的，能夠讓APP進到OS，讓OS做APP想做的事。

Advantages of assembly program than high-level program
+ Small code size `程式小`
+ Useful for limited memory space
+ Short execution time `執行快`
+ Useful for real-time application or time-sensitive application
+ Low level control `I/O控制，高階語言很難做到`
+ Device service routines

OS的程式
+ C：95%
+ 組合語言：5%

Assembly language program development on the PC
---


The Instruction set
---
`117 basic instructions` for the 8088/8086
+ Data transfer
+ Mov, push, pop, XCHG(exchange), in, out, ...
> XCHG：register直接交換，不用多設變數
+ Arithmetic
+ Add, adc, inc, sub, sbb, dec, cmp, ...
> inc：++，sbb：--
+ Logic
+ And, or, not, shift, rotate, test, xor, ...
+ String manipulation
+ Rep, movs, cmps, ...
> Rep：重複
+ Control transfer
+ Call, ret, jmp, conditional jump, loop, conditional loop, int, ...
+ Processor control
+ Clc, cmc, stc, cli, (set and reset flag), ...

The MOV instruction
---
### MOV D, S
> D：(Destination)目的，S：(Source)來源。來源的值`copy`一份到目的


+ Memory
+ `[]`：記憶體，內部的值很像arr[index]的概念。
+ Accumulator (AX)
+ Register
+ Seg-reg (區段暫存器)
+ Reg16 (DX)
+ Immediate (立即值)

Example：
1. MOV AL, '0'
+ AL：register
+ '0'：immediate
2. MOV [400], AL
+ []：memory
+ AL：register
3. MOV BL, [400]
+ BL：register
+ []：memory
4. MOV [402], 02
+ []：memory
+ 02：immediate
5. ADD AL, BL
+ AL <- AL + BL
6. SUB AL, CL
+ AL <- AL - CL


> 把CS的值複製一份到DX

Addressing mode 定址模式
---
CPU找到資料的方式，稱作定址模式。

Access different type of operands, the 8088 is provided with various addressing modes.
+ `Register` addressing mode
+ `Immediate` addressing mode
+ `Memory` addressing mode
+ Direct
+ Register indirect
+ Based
+ Indexed
+ Based-Indexed


---
### Register operand addressing mode

MOV AX, BX



> Data在register裡，不用到memory裡拿，也就是說不用去算實體位址。

---
### Immediate operand addressing mode

MOV AL, 15H



> Data在指令中裡，可立即拿到，不在register也不在memory，也就是因為不在memory裡，所以就不用去算實體位址。

---
### Memory operand addressing mode

`Physical address (PA)` is computed from a segment base address (SBA) and an effective address (EA)
> 資料在memory裡，所以要去算**實體位址**

Five memory operand addressing modes
+ Displacement：Direct addressing mode
+ BX, BP, SI, DI：Register indirect
+ BX or BP + displacement：Based
+ SI or DI + displacement：Indexed
+ BX, BP + SI, DI + displacement：Based-Indexed

> Based和Indexed，很像，差別在用的register不同


**Direct Addressing Mode**

MOV CX, [1234H]



> PA = SBA * 16 + EA
> 為何是用DS(Data segment)算呢？因為資料在資料區，所以是用DS算。

**Register Inderict Addressing Mode**

MOV AX, [SI]



**Based Addressing Mode**
> 常用在一維陣列

MOV [BX] + 1234H, AL



**Indexed Addressing Mode**

MOV AL, [SI] + 1234H


**Based-Indexed Addressing Mode**
> 常用在二維陣列

MOV AH, [BX][SI] + 1234H



參考資料
+ Barry B. Bery, “The Intel Microprocessors,” 8th Edition, 2009, Prentice Hall.
+ Walter A. Triebel, Avtar Singh, “The 8088 and 8086 Microprocessors – Programming, Interfacing, Software, Hardware, and Applications,” 4th Edition, 2003, Prentice Hall.
+ 國立臺北大學資工系張玉山教授ppt