王爽《汇编语言》(第三版)实验16解析

安装程序

assume cs:code 
code segment 

start:	mov ax,cs
		mov ds,ax
		mov si,offset setscreen
		mov ax,0
		mov es,ax
		mov di,200h
		mov cx,offset setscreenend-offset setscreen
		cld
		rep movsb
		
		mov ax,0
		mov es,ax
		mov word ptr es:[7ch*4],200h
		mov word ptr es:[7ch*4+2],0
		
		mov ax,4c00h
		int 21h

setscreen:
			cmp ah,0	; 清屏
			je do1
			cmp ah,1	; 设置前景色
			je do2
			cmp ah,2	; 设置背景色
			je do3
			cmp ah,3	; 向上滚动一行
			je do4
			jmp short sret
		
		do1:call sub1
			jmp short sret
		do2:call sub2
			jmp short sret
		do3:call sub3
			jmp short sret
		do4:call sub4
		
		sret: ret
		
	sub1:	push bx
			push cx
			push es
			
			mov bx,0b800h
			mov es,bx
			mov bx,0
			mov cx,2000
	sub1s:	mov byte ptr es:[bx],' '
			add bx,2
			loop sub1s
			
			pop es
			pop cx
			pop bx
			ret
		
	sub2:	push bx
			push cx
			push es
			
			mov bx,0b800h
			mov es,bx
			mov bx,1
			mov cx,2000
	sub2s:	and byte ptr es:[bx],11111000b
			or es:[bx],al
			add bx,2
			loop sub2s
			
			pop es
			pop cx
			pop bx
			ret
		
	sub3:	push bx
			push cx
			push es
			
			mov cl,4
			shl al,cl
			mov bx,0b800h
			mov es,bx
			mov bx,1
			mov cx,2000
	sub3s:	and byte ptr es:[bx],10001111b
			or es:[bx],al
			add bx,2
			loop sub3s
			
			pop es
			pop cx
			pop bx
			ret
		
	sub4:	push cx
			push si
			push di			
			push es
			push ds
			
			mov si,0b800h
			mov es,si
			mov ds,si
			mov si,160
			mov di,0
			cld
			mov cx,24
			
	sub4s:	push cx
			mov cx,160
			rep movsb
			pop cx
			loop sub4s
			
			mov cx,80
			mov si,0
	sub4s1:	mov byte ptr [160*24+si],' '	;最后一行清空
			add si,2
			loop sub4s1
			
			pop ds 
			pop es
			pop di
			pop si
			pop cx
			ret
setscreenend: nop

code ends
end start

测试

assume cs:code

code segment
		
start:	;mov ah,0	;清屏
		
		;mov ah,1
		;mov al,7	; 设置前景色，al为颜色
		
		;mov ah,2
		;mov al,7	; 设置背景色，al为颜色
		
		;mov ah,3	; 向上滚动一行
		int 7ch
		
		mov ax,4c00h
		int 21h
code ends

end start