--开始位检测
process(clk,cs_n,idle)
variable counta:std_logic_vector(3 downto 0);
begin
if(cs_n='0')then
counta:="0000";
work_op<='0';--0:不接受数据
else
if(idle='0')then
work_op<='1';
counta:="0000";
else
if(clk'event and clk='0') then
case counta is
when "1100"=>work_op<='1';
when others=>if(rs232_din='0')then
counta:=counta+1;
else
counta:="0000";
end if;
work_op<='0';
end case;
end if;
end if;
end if; 这是我串口检测信号的程序，差不多，你看看吧，应该有帮助的吧 | 
