scan8.vhd

在FPGA上实现的出租车计价器VHDL源代码

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;
entity scan8 is
  port (clk : in std_logic;
        a,b,c,d,e,f,g,h : in std_logic_vector(7 downto 0);
		  pa,pb,pc,pd,pe,pf,pg,ph : out std_logic;
		  mux_out :out std_logic_vector(7 downto 0) );
end scan8;
architecture arch of scan8 is
  signal sel : std_logic_vector(2 downto 0):="000";
begin
  process(clk,a,b,c,d,e,f,g,h)
  begin
    --if rst='1' then sel<="000";
	   if rising_edge(clk) then
	      --if sel = "110" then
	       --  sel<= "000";
	       --  mux_out <= a;
	       --  pa<='0';pb<='1';pc<='1';pd<='1';pe<='1';pf<='1';			          
	      -- else  
	       -- sel<=sel + "001";	 
		   -- end if; 	      
		   case sel is
		     when "000" => mux_out <= a;
			                pa<='0';pb<='1';pc<='1';
			                pd<='1';pe<='1';pf<='1';pg<='1';ph<='1';
		     when "001" => mux_out <= b;
			                pa<='1';pb<='0';pc<='1';
			                pd<='1';pe<='1';pf<='1';pg<='1';ph<='1';
		     when "010" => mux_out <= c;
			                pa<='1';pb<='1';pc<='0';
			                pd<='1';pe<='1';pf<='1';pg<='1';ph<='1';
		     when "011" => mux_out <= d;
			                pa<='1';pb<='1';pc<='1';
			                pd<='0';pe<='1';pf<='1';pg<='1';ph<='1';
			  when "100" => mux_out <= e;
			                pa<='1';pb<='1';pc<='1';
			                pd<='1';pe<='0';pf<='1';pg<='1';ph<='1';
			  when "101" => mux_out <= f;
			                pa<='1';pb<='1';pc<='1';
			                pd<='1';pe<='1';pf<='0';pg<='1';ph<='1';
			  when "110" => mux_out <= g;
			                pa<='1';pb<='1';pc<='1';
			                pd<='1';pe<='1';pf<='1';pg<='0';ph<='1';
			  when "111" => mux_out <= h;
			                pa<='1';pb<='1';pc<='1';
			                pd<='1';pe<='1';pf<='1';pg<='1';ph<='0';
			  when others => mux_out <= "11111111";
			                pa<='1';pb<='1';pc<='1';
			                pd<='1';pe<='1';pf<='1';pg<='1';ph<='1';
		  end case;
		   sel<=sel + "001";
	 end if;
  end process;
end arch;