main:
ldi r16,0x00
out ucsra,r16
out ucsrb,r16 //初始化控制与状态寄存器A、B
ldi r16,0x86
out ucsrc,r16 //选择ucsrc寄存器,异步模式,禁止校验,8位数据
ldi r16,0x00
out ubrrh,r16
ldi r16,0x2f
out ubrrl,r16 //设置波特率位9600
ldi r16,0x98
out ucsrb,r16 //接收中断使能
sei
ldi r16,0x02
out ddrd,r16