Assembly Language Programming notes

Compilation Study NOTE 1

Study Bibliography "assembly language" second Edition engineering machinery Industry Press

Suppose x=4,y=5,z= ((x+y) *8-x)/2. Write a assembler program to implement the formula calculation:

DATAS SEGMENT
    x DW 4  ; define x as a word cell with a value of 4
    Y DW 5
    Z DW?  ; Define Z as empty cell
DATAS ENDS

STACKS SEGMENT
    ; Enter stack segment code
STACKS ENDS
    CODES SEGMENT assume Cs:codes,ds :D atas,ss:stacks
START:
    mov ax,datas
    mov ds,ax
   
    mov bx,x
    mov ax,y
    ADD ax,bx  ; addition
    MOV cl,3
    SAL ax,cl   ; arithmetic left 3 bits, equivalent to multiplying by 8
    SUB ax,x
    SAR ax,1     ; arithmetical right shift one bit, equivalent to dividing by 2
    mov z,ax
    mov z,ax
    
    mov Ah,4ch
    INT 21H
CODES ENDS
    END START

Meaning:

1) x, Y, z these three variables should be considered as storage units, symbolic addresses

2) Describe the relationship between the segment register and the segment name using the assume pseudo-directive

3) START represents the offset address of the unit where the assembly instruction MOV Ax,datas is located, and the logical instruction of the instruction is Cs:start

4) INT 21H is the DOS interrupt call instruction; the function of 4CH is to end the program and return DOS

(1) Disassembly instruction U

The first instruction logical address 0b52:0000, that is, is specified from the code snippet NO. 0 Unit start storage;

If the program is longer and one screen does not appear, you should press the U instruction until the last instruction of the program appears (

MOV ah,4ch

INT 21H

）

(2) Execute program command g

The G command can execute the instruction continuously until the breakpoint is given.

AX=4C22, of which ah=4c, should be caused by movah,4ch;

(3) View storage Unit Command D

View storage Unit Commands D

X, y, z are defined in the program are the word units, so the two bytes as a word unit;

So, 0004 in unit 1th and No. 0 is the value of X, and 2nd in unit 3rd and 0005 is the value of Y, and

The value of z is 0022 in unit 5th and unit 4th;

(4) exit the debug command Q

After executing the q command, exit debug to return DOS;