汇编中的大小写转换

分析：

‘a’=1010001

‘A’=1000001

当第五位为1时是小写，为0位大写

小写转大写用到按位与运算

;小写转大写
assume cs:code,ds:data
data segment
    db 'BaSic'
data ends

code segment
    start:
        mov ax,data
        mov ds,ax
        mov cx,5
        mov bx,0
        s:
            mov al,[bx]
            and al,11011111b
            mov [bx],al
            inc bx
            loop s
        mov ax,4c00h
        int 21h
code ends
end start

大写转小写用到按位或运算

;大写转小写
assume cs:code,ds:data
data segment
    db 'BaSic'
data ends

code segment
    start:
        mov ax,data
        mov ds,ax
        mov cx,5
        mov bx,0
        s:
            mov al,[bx]
            and al,11011111b
            mov [bx],al
            inc bx
            loop s
        mov ax,4c00h
        int 21h
code ends
end start