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)
	begin
		if (rising_edge(CLK_I)) then
			if (T2 = '1') then
				if    (CLR = '1') then		LPC     <= X"0000";
				elsif (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 if;
		end if;
	end process;
 
end Behavioral;