Sunday, September 28, 2008

VHDL PROGRAM OF A4013B_vhd

-- ============================================================================
-- 4013B Dual D-type Flip Flop
--
-- Copyright (C),2004 Andrew John Jacobs.
--
-- This program is provided free of charge for educational purposes
--
-- Redistribution and use in binary form without modification, is permitted
-- provided that the above copyright notice, this list of conditions and the
-- following disclaimer in the documentation and/or other materials provided
-- with the distribution.
--
-- THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS 'AS IS' AND ANY
-- EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
-- WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
-- DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY
-- DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
-- (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
-- LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
-- ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-- (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
-- THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-- ============================================================================

library ieee;
use ieee.std_logic_1164.all;

entity A4013B is
generic (
tplh : time := 0 ns;
tphl : time := 0 ns);
port (
s1 : in std_logic; -- Set
c1 : in std_logic; -- Clear
d1 : in std_logic; -- Data
cp1 : in std_logic; -- Clock
s2 : in std_logic;
c2 : in std_logic;
d2 : in std_logic;
cp2 : in std_logic;
o1 : out std_logic; -- Output
o1_n : out std_logic; -- Output inverted (usually)
o2 : out std_logic;
o2_n : out std_logic);
end entity;

-- ============================================================================

-- NB.
--
-- If either or both of the set/clear inputs change then the output will
-- asynchronously update. Only if both are clear is the state of the data
-- input latched and inverted on the rising edge of the next clock pulse.

library ieee;
use ieee.std_logic_1164.all;
library work;

architecture behaviour of A4013B is
-- Internal flip flop states
signal ff1 : std_logic_vector (1 to 2);
signal ff2 : std_logic_vector (1 to 2);
begin
-- Flip flop 1
process (cp1,s1,c1)
begin
if ((s1 or c1) = '1') then
ff1(1) <= s1;
ff1(2) <= c1;
elsif rising_edge(cp1) then
ff1(1) <= d1;
ff1(2) <= not d1;
end if;
end process;

-- Flip flop 2
process (cp2,s2,c2)
begin
if ((s2 or c2) = '1') then
ff2(1) <= s2;
ff2(2) <= c2;
elsif rising_edge(cp2) then
ff2(1) <= d2;
ff2(2) <= not d2;
end if;
end process;

-- Copy state to outputs adding propagation delay
o1 <= '1' after tplh when to_bit(ff1(1)) = '1' else
'0' after tphl;
o1_n <= '1' after tplh when to_bit(ff1(2)) = '1' else
'0' after tphl;

o2 <= '1' after tplh when to_bit(ff2(1)) = '1' else
'0' after tphl;
o2_n <= '1' after tplh when to_bit(ff2(2)) = '1' else
'0' after tphl;
end architecture;

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