王爽汇编语言第二版学习笔记之实验11

assume cs:codesg

datasg segment
    db "Beginner's All-purpose Symbolic Instruction Code.",0
datasg ends

codesg segment
begin:
    mov ax,datasg
    mov ds,ax
    mov si,0
    call letterc
    
    mov ax,4c00h
    int 21h
    
letterc:
    push cx
    push si
    push bx
    
    mov cx,0
ks:    
    mov byte ptr cl,ds:[si]
    jcxz ok
    cmp cl,97
    jb lp
    cmp cl,122
    ja lp
    and cl,11011111B
    mov byte ptr ds:[si],cl
lp:
    inc si
    jmp short ks
ok:
    pop bx
    pop si
    pop cx
    ret
    
codesg ends
end begin