assume cs:code

data segment
        db 'Welcome to masm!',0
data ends

code segment
start:
        mov dh,24
        mov dl,0
        mov cl,2
        mov ax,data
        mov ds,ax
        mov si,0
        call show_str

        mov ax,4c00H
        int 21H

; 名称：show_str
; 功能：在指定的位置，用指定的颜色，显示一个用0结束的字符串
; 参数: (DH)=行号(取值范围为0-24);
;                (DL)=列号(取值范围为0-79);
;                (Cl)=颜色;ds:si指向字符串的首地址
show_str:
                ; 保存现场
                push ax
                push es
                push dx
                push cx
                push ds
                push bx ; 偏移量指针
                mov ax,0b800H
                mov es,ax
                
                ; 显示位置的偏移量计算公式为：(行号 - 1) * 160 + 列号
                ;sub dh,1
                mov al,dh
                mov ah,0
                mov dh,0
                mov bl,160
                mul bl
                add dl,dl
                add ax,dx
                
                mov bx,ax  ; 显示字符串的偏移量存放到(bX)中
                
s:                mov dl,[si]
                mov dh,cl
                mov es:[bx],dx
                mov ch,0
                mov cl,dl
                jcxz ok
                inc si
                add bx,2
                jmp short s
                
ok:                pop bx
                pop ds
                pop cx
                pop dx
                pop es
                pop ax
                ret
code ends

end start