selection.vhd

本程序是用VHDL语言实现异步通信控制器

LIBRARY ieee; 
USE ieee.std_logic_1164.all;
USE ieee.std_logic_unsigned.all;
entity selection is
	port(CS,A0,RD,WR:IN STD_LOGIC;
		 Rx_buf:IN STD_LOGIC_VECTOR(7 DOWNTO 0);
		 status:IN STD_LOGIC_VECTOR(7 DOWNTO 0);
		 Tx_buf:OUT STD_LOGIC_vector(7 DOWNTO 0);
		 D:INOUT STD_LOGIC_VECTOR(7 DOWNTO 0));
END;
ARCHITECTURE behavior of selection is
begin
process
  begin	
	IF (CS='0' AND RD='0' AND WR='1') THEN
		IF A0='0' THEN
			D<=Rx_buf;
		ELSE
			D<=status;
		END IF;
	ELSIF CS='0' AND RD='1' AND WR='0' THEN
		TX_buf<=D;D<="ZZZZZZZZ";
	ELSE D<="ZZZZZZZZ";   
	end if; 
end process;
end;