源代码：
program segment
main proc far
assume cs:program
start:
push ds
sub ax,ax
push ax
mov ch,4
roate: mov cl,4
rol bx,cl
mov al,bl
and al,0fh
add al,30h
cmp al,3ah
jl printit
add al,7h
printit:
mov dl,al
mov ah,2
int 21h
dec ch
jnz roate
ret
main endp
program ends
end
