Chapter VII & assembly language experiment six
7.1 and and or instructions
and instructions, and logic instructions perform bitwise AND
mov al,01100011B
and al,00111011B
After executing al = 00100011B, by the instruction of the operation target corresponding bit may be set to 0, the other bits unchanged
or instructions, logic or instructions, bitwise OR operation
mov al,01100011B
or al,00111011B
After executing al = 01111011B, by the instruction of the operation target corresponding bit may be set to 1, the other bits unchanged
About 7.2 ASCII code
We put the information stored in the computer, it is necessary it is encoded into binary information, and the information will be stored in a computer display to us, it is necessary to decode, ASCII code is an encoding scheme
When editing text Press a key, this key information incoming PC, into the computer code stored in the memory 61H, 61H text editing software taken from memory, it is sent to the memory on the video card, the work in the text the graphics mode, the contents of display memory used to explain the rules of the ASCII code, 61H is treated as a character, a character driving the display graphics image drawn on the screen
7.3 Data given in characters
In assembler, with '......' manner specified character data in the form given by the compiler converting them to the corresponding ASCII code
assume cs:code,ds:date
data segment
db 'unIX'
db 'foRK'
data ends
code segment
start: mov al,'a'
mov bl,'b'
mov ax,4c00h
int 21h
code ends
end start
db 'unIX' equivalent 'db 75H, 6EH, 49H, 58H'
mov al, 'a' corresponds mov al, 61H
7.4 case conversion issues
The first string is converted to uppercase datasg, the second string into lowercase
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The first method, observed lowercase ASCII value than the large capital letters ASCII value corresponding to 20H, but due to the lower case string both have uppercase, determines whether the required upper or lower case, but not learned compilation of statements by using judgment
The second method, from the point of view of ASCII code binary form, except bit 5 (counting from 0), the other bits are the same, so for a letter, regardless of uppercase lowercase, the first position 5 can be zero
assume cs:codesg,ds:datasg
datasg segment
db 'BaSiC'
db 'iNdOrMaTiOn'
datasg ends
codesg sgement
start: mov ax,datasg
mov ds,ax
mov bx,0
mov cx,0
s:mov al,[bx]
and al,11011111B
mov [bx],al
inc bx
loop s
mov bx,5
mov cx,11
s0:mov al,[bx]
or al,00100000B
mov [bx],al
inc bx
loop s0
mov ax,4c00h
int 21h
codesg ends
end start
7.5 [bx + data]
A memory cell may be represented by [bx + idata], which offset address is (bx) + idata
The following instruction is equivalent to
mov ax,[bx+200]
mov ax.[200+bx]
mov ax,200[bx]
mov ax,[bx].200
Array processing with 7.6 [bx + idata] manner
Fill code codesg, the first string into a defined datasg uppercase, lowercase string into a second
The original method requires two cycles, but at the same cycle can be completed in
assume cs:code,ds:datasg
datasg segment
db 'BaSiC'
db 'MinIX'
datasg ends
codesg segment
start: mov ax,datasg
mov ds,ax
mov bx,0
mov cx,5
s:mov al,[bx]
and al,11011111B
mov [bx],al
mov al,[5+bx]
or al,00100000B
mov [5+bx],al
inc bx
loop s
mov ax,4c00H
int 21H
codesg ends
end
Comparison of c and assembly language
C：a[i],b[i]
Compilation: 0 [bx], 5 [bx]
7.7 和 OF YOU
8086CPU si and di are similar in function and register bx, si, and di is divided into two 8-bit registers can not be used
3 the same set of instructions following features
mov bx,0
mov ax,[bx]
mov si,0
mov ax,[si]
mov di,0
mov ax,[di]
Di si and implemented with the string 'welcome to masm!' Copy back to its data area
assume cs:codesg,ds:datasg
datasg segment
db 'welcome to masm!'
db '................'
datasg ends
codesg sgement
start: mov ax,datasg
mov ds,ax
mov si,0
mov cx,8
s:mov ax,0[si]
mov 16[si],ax
add si,2
loops
mov ax,4c00h
int 21h
codesg ends
end start
7.8 [bx + si] 和 [bx_di]
[Bx + di] i.e. offset address (bx) + (si)
The following instruction is equivalent to
mov ax,[bx+si]
mov ax,[bx][si]
7.9 [+ bx + is idata] 和 [bx + of + idata]
[Bx + si + idata] 即 (x) + (yes) + idata
Common formats
mov ax,[bx+si+200]
mov ax,[bx+200+si]
mov ax,[200+bx+si]
mov ax,200[bx][si]
mov ax,[bx].200[si]
mov ax,[bx][si].200
7.10 flexible application of different ways of addressing
The first letter of each word in datasg paragraph to uppercase letters
assume cs:codesg,ds:datasg
datasg segment
db '1. file ' ;每个字符串长度为16个字节，因为连续存放
db '2. edit ' ;加空格保证两个字符串不在同一个段中
db '3. search '
db '4 .view '
db '5. options '
db '6. help '
datasg ends
codesg segment
start: mov ax,datasg
mov ds,ax
mov bx,0
mov cx,6
s:mov al,[bx+3]
and al,11011111B
mov [bx+3],al
add bx,16
loops
mov ax,4c00h
int 21h
codesg ends
end start
The segment of each word in datasg uppercase letters, so we must use two heavy cycle, but should be used cx two cycles, it is necessary outer loop cx temporary value of the temporary register may be used, but generally to say, when needed temporary storage of data, we should use the stack
assume cs:codesg,ds:datasg,ss:stacksg
datasg segment
db 'ibm '
db 'dec '
db 'dos '
db 'vax '
datasg ends
stacksg segment
dw 0,0,0,0,0,0,0,0 ;定义一共栈段，容量为16个字节
stacksg ends
codesg segment
start: mov ax,stacksg
mov ss,ax
mov sp,16
mov ax,datasg
mov ds,ax
mov bx,0
mov cx,4
s0:push cx ;外层循环的cx压栈
mov si,0
mov cx,3
s:mov al,[bx+si]
and al,11011111B
mov [bx+si],al
inc si
loops
add bx,16
pop cx
loop s0
mov ax,4c00h
int 21h
codesg ends
end start
Sixth experiment
Program, the first four letters of each word in datasg paragraph to uppercase letters
assume cs:codesg,ss:stacksg,ds:datasg
stacksg segment
dw 0,0,0,0,0,0,0,0
stacksg ends
datasg segment
db '1. display '
db '2. brows '
db '3. replace '
db '4. modify '
datasg ends
codesg segment
start: mov ax,stacksg
mov ss,ax
mov sp,16
mov ax,datasg
mov ds,ax
mov bx,0
mov cx,4
s0:push cx
mov si,3
mov cx,4
s0:push cx
mov si,3
mov cx,4
s:mov al,[bx+si]
and al,11011111B
mov [bx+si],al
inc si
loop s
pop cx
add bx,16
loop s0
mov ax,4c00h
int 21h
codesg ends
end start
