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[/] [System09/] [trunk/] [rtl/] [VHDL/] [ACIA_Clock.vhd] - Blame information for rev 138

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Line No. Rev Author Line
1 99 davidgb
--===========================================================================--
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--                                                                           --
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--  ACIA_Clock.vhd - Synthesizable Baud Rate Clock Divider                   --
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--                                                                           --
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--===========================================================================--
6 19 dilbert57
--
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--  File name      : ACIA_Clock.vhd
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--
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--  Purpose        : Implements a baud rate clock divider for a 6850 compatible
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--                   Asynchronous Communications Interface Adapter 
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--                  
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--  Dependencies   : ieee.std_logic_1164
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--                   ieee.std_logic_arith
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--                   ieee.std_logic_unsigned
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--                   ieee.numeric_std
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--                   work.bit_funcs
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--
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--  Author         : John E. Kent
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--
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--  Email          : dilbert57@opencores.org      
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--
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--  Web            : http://opencores.org/project,system09
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--
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--  ACIA_Clock.vhd is baud rate clock divider for a 6850 compatible ACIA core.
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-- 
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--  Copyright (C) 2003 - 2010 John Kent
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--
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--  This program is free software: you can redistribute it and/or modify
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--  it under the terms of the GNU General Public License as published by
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--  the Free Software Foundation, either version 3 of the License, or
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--  (at your option) any later version.
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--
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--  This program is distributed in the hope that it will be useful,
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--  but WITHOUT ANY WARRANTY; without even the implied warranty of
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--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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--  GNU General Public License for more details.
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--
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--  You should have received a copy of the GNU General Public License
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--  along with this program.  If not, see <http://www.gnu.org/licenses/>.
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--
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--===========================================================================--
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--                                                                           --
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--                              Revision  History                            --
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--                                                                           --
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--===========================================================================--
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--
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-- Revision Name          Date             Description
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-- 0.1      John Kent     unknown          Initial version
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-- 1.0      John Kent     30th May 2010    Added GPL header 
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--      
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52 19 dilbert57
library ieee;
53 99 davidgb
   use ieee.std_logic_1164.all;
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   use ieee.std_logic_arith.all;
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   use ieee.std_logic_unsigned.all;
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   use ieee.numeric_std.all;
57 118 dilbert57
--library unisim;
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--      use unisim.vcomponents.all;
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library work;
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   use work.bit_funcs.all;
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entity acia_clock is
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  generic (
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     SYS_CLK_FREQ  : integer;
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          ACIA_CLK_FREQ : integer
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  );
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  port(
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    clk      : in  Std_Logic;  -- System Clock input
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         acia_clk : out Std_Logic   -- ACIA Clock output
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  );
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end acia_clock;
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-------------------------------------------------------------------------------
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-- Architecture for ACIA_Clock
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-------------------------------------------------------------------------------
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architecture rtl of ACIA_Clock is
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constant FULL_CYCLE : integer :=  (SYS_CLK_FREQ / ACIA_CLK_FREQ);
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constant HALF_CYCLE : integer :=  (FULL_CYCLE / 2);
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signal   acia_count : Std_Logic_Vector(log2(FULL_CYCLE) downto 0) := (Others => '0');
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begin
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--
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-- Baud Rate Clock Divider
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--
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-- 25MHz / 27  = 926,000 KHz = 57,870Bd * 16
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-- 50MHz / 54  = 926,000 KHz = 57,870Bd * 16
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--
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my_acia_clock: process( clk  )
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begin
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    if(clk'event and clk = '0') then
92 99 davidgb
                if( acia_count = (FULL_CYCLE - 1) )     then
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                        acia_clk   <= '0';
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                   acia_count <= (others => '0'); --"000000";
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                else
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                   if( acia_count = (HALF_CYCLE - 1) )  then
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                                acia_clk <='1';
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                        end if;
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                   acia_count <= acia_count + 1;
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                end if;
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    end if;
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end process;
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end rtl;

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