Subversion Repositories c16

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.STD_LOGIC_ARITH.ALL;

use IEEE.STD_LOGIC_UNSIGNED.ALL;

--  Uncomment the following lines to use the declarations that are

--  provided for instantiating Xilinx primitive components.

--library UNISIM;

--use UNISIM.VComponents.all;

use work.cpu_pack.ALL;

entity opcode_fetch is

        Port(   CLK_I  : in  std_logic;

                        T2     : in  std_logic;

                        CLR    : in  std_logic;

                        CE     : in  std_logic;

                        PC_OP  : in  std_logic_vector( 2 downto 0);

                        JDATA  : in  std_logic_vector(15 downto 0);

                        RR     : in  std_logic_vector(15 downto 0);

                        RDATA  : in  std_logic_vector( 7 downto 0);

                        PC     : out std_logic_vector(15 downto 0)

                );

end opcode_fetch;

architecture Behavioral of opcode_fetch is

        signal  LPC  : std_logic_vector(15 downto 0);

        signal  LRET : std_logic_vector( 7 downto 0);

begin

        PC <= LPC;

        process(CLK_I, CLR)

        begin

                if (CLR = '1') then

                        LPC     <= X"0000";

                elsif ((rising_edge(CLK_I) and T2 = '1') and CE = '1' ) then

                        case PC_OP is

                                when PC_NEXT =>         LPC  <= LPC + 1;                -- next address

                                when PC_JMP  =>         LPC  <= JDATA;                  -- jump address

                                when PC_RETL =>         LRET <= RDATA;                  -- return address L

                                                                        LPC  <= LPC + 1;

                                when PC_RETH =>         LPC  <= RDATA & LRET;   -- return address H

                                when PC_JPRR =>         LPC  <= RR;

                                when PC_WAIT =>

                                when others  =>         LPC  <= X"0008";                -- interrupt

                        end case;

                end if;

        end process;

end Behavioral;