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--!

--! PDP8 Processor

--!

--! \brief

--!      CPU Power-On Trap (PWRTRP) Register

--!

--! \details

--!      The Power-On Trap (PWRTRP) Register is association with

--!      the STARTUP input is used to control the startup

--!      operation of the CPU.

--!

--!      The PWRTRP Register is defined in the HD-6120

--!      documentation.

--!

--!      When the unit is configured as a HD-6120, the PWRTRP

--!      Register will be set to the state of STARTUP input

--!      when the reset input is negated.

--!

--!      If the PWRTRP register is set, the unit will boot

--!      to the Normal Mode Boot Vector (Address 0000).

--!      Otherwise the unit will boot to the Panel Mode

--!      Boot Vector (Address 7777)

--!

--! \todo

--!      Probably don't need this register.  Delete it.

--!      Just initialize the PC dependant on the STARTUP

--!      input to 0000 or 7777.

--!

--! \file

--!      pwrtrp.vhd

--!

--! \author

--!      Rob Doyle - doyle (at) cox (dot) net

--!

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--

--  Copyright (C) 2009, 2010, 2011 Rob Doyle

--

-- This source file may be used and distributed without

-- restriction provided that this copyright statement is not

-- removed from the file and that any derivative work contains

-- the original copyright notice and the associated disclaimer.

--

-- This source file is free software; you can redistribute it

-- and/or modify it under the terms of the GNU Lesser General

-- Public License as published by the Free Software Foundation;

-- version 2.1 of the License.

--

-- This source is distributed in the hope that it will be

-- useful, but WITHOUT ANY WARRANTY; without even the implied

-- warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR

-- PURPOSE. See the GNU Lesser General Public License for more

-- details.

--

-- You should have received a copy of the GNU Lesser General

-- Public License along with this source; if not, download it

-- from http://www.gnu.org/licenses/lgpl.txt

--

--------------------------------------------------------------------

--

-- Comments are formatted for doxygen

--

library ieee;                                   --! IEEE Library

use ieee.std_logic_1164.all;                    --! IEEE 1164

use work.cpu_types.all;                         --! Types

--

--! CPU Power-On Trap (PWRTRP) Register Entity

--

entity ePWRTRP is port (

    sys      : in  sys_t;                       --! Clock/Reset

    pwrtrpOP : in  pwrtrpop_t;                  --! PWRTRP Operation

    PWRTRP   : out std_logic                    --! PWRTRP Output

);

end ePWRTRP;

--

--! CPU Power-On Trap (PWRTRP) Register RTL

--

architecture rtl of ePWRTRP is

    signal pwrtrpREG : std_logic;               --! Power On Trap Flip-Flop

    signal pwrtrpMUX : std_logic;               --! Power On Trap Flip-Flop Multiplexer

begin

    --

    -- PWRTRP Multiplexer

    --

    with pwrtrpOP select

        pwrtrpMUX <= pwrtrpREG when pwrtrpopNOP,

                    '0'        when pwrtrpopCLR,

                    '1'        when pwrtrpopSET;

    --

    --! PWRTRP Register

    --

    REG_PWRTRP : process(sys)

    begin

        if sys.rst = '1' then

            pwrtrpREG <= '0';

        elsif rising_edge(sys.clk) then

            pwrtrpREG <= pwrtrpMUX;

        end if;

    end process REG_PWRTRP;

    PWRTRP <= pwrtrpREG;

end rtl;