pc.vhd

在软件MAX+plus II环境中

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_ARITH.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
ENTITY PC IS
PORT(
       LOAD,LDPC,CLR:IN STD_LOGIC;
       D:IN STD_LOGIC_VECTOR(7 DOWNTO 0);
      O:OUT STD_LOGIC_VECTOR(7 DOWNTO 0)
       );
END PC;
ARCHITECTURE A OF PC IS
SIGNAL QOUT: STD_LOGIC_VECTOR(7 DOWNTO 0);
BEGIN
       PROCESS(LDPC,CLR,LOAD)
       BEGIN
              IF (CLR='0')  THEN  --pc=0
                     QOUT<= "00000000";
              ELSIF (LDPC'EVENT AND LDPC='1') THEN
                     IF (LOAD='0') THEN
                            QOUT<=D;  --BUS->PC
                     ELSE
                            QOUT<= QOUT+1;     --PC+1
                     END IF;
              END IF;
       END PROCESS;
       O<= QOUT;
END A;