《汇编语言》（王爽）学习笔记---实验十一（编写子程序）

assume cs:codesg

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

stack segment
    db 16 dup(0)
stack ends

codesg segment
begin:
	mov ax,stack
	mov ss,ax
	mov sp,16
	mov ax,datasg
	mov ds,ax
	mov si,0
	call letterc

	mov ax,4c00h
	int 21h

letterc:
	pushf
	push cx
	push si
	
s:
	mov ch,0
	mov cl,ds:[si]
	jcxz exit
	cmp byte ptr ds:[si],61h
	jb next_char
	cmp byte ptr ds:[si],7Ah
	ja next_char
	and byte ptr ds:[si],11011111B
	
next_char:
	inc si
	
	jmp short s
	
exit:
	pop si
	pop cx
	popf
	ret
codesg ends
end begin