汇编语言(王爽)--实验11 编写子程序

assume cs:code,ds:data

data segment
	db "Beginner's All-purpose Symbolic Intruction Code.",0
data ends

code segment
start:
	mov ax,data
	mov ds,ax
	mov si,0
	call letterc
	
	mov ax,4c00h
	int 21h
	
letterc:
	mov al,[si]
	;小写字母的ascii范围[97,122]
	cmp al,97  ;小于97 循环到下一次
	jb s
	cmp al,122 ;大于122,循环到下一次
	ja s
	and al,11011111b
	mov [si],al
s:	inc si
	cmp al,0
	jne letterc
	ret

code ends
end start