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----------------------------------------------------------------------------------
-- Company:
-- Engineer:
--
-- Create Date: 05/03/2025 03:20:07 PM
-- Design Name:
-- Module Name: Fct_2_3 - Behavioral
-- Project Name:
-- Target Devices:
-- Tool Versions:
-- Description:
-- Multiply a 4 bit number and get an approximation.
-- Works for 0 to 12, it's off above.
-- 12 is the highest good input value because of thermometric 12 bits encoding.
-- Dependencies:
--
-- Revision:
-- Revision 0.01 - File Created
-- Additional Comments:
--
----------------------------------------------------------------------------------
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
-- Uncomment the following library declaration if using
-- arithmetic functions with Signed or Unsigned values
--use IEEE.NUMERIC_STD.ALL;
-- Uncomment the following library declaration if instantiating
-- any Xilinx leaf cells in this code.
--library UNISIM;
--use UNISIM.VComponents.all;
entity Fct_2_3 is
Port ( ADCbin : in STD_LOGIC_VECTOR (3 downto 0);
A2_3 : out STD_LOGIC_VECTOR (2 downto 0));
end Fct_2_3;
architecture Behavioral of Fct_2_3 is
signal shifted_once : STD_LOGIC_VECTOR(3 downto 0);
signal shifted_twice : STD_LOGIC_VECTOR(3 downto 0);
signal shifted_thrice : STD_LOGIC_VECTOR(3 downto 0);
signal carry_in : STD_LOGIC;
signal carry_out : STD_LOGIC;
signal added : STD_LOGIC_VECTOR(3 downto 0);
component Add4Bits is
Port ( A : in STD_LOGIC_VECTOR (3 downto 0);
B : in STD_LOGIC_VECTOR (3 downto 0);
C : in STD_LOGIC;
R : out STD_LOGIC_VECTOR (3 downto 0);
Rc : out STD_LOGIC);
end component;
begin
-- N x 2^-1 : shifted once
shifted_once <= '0' & ADCbin(3 downto 1);
-- N x 2^-3 : shifted thrice
shifted_twice <= '0' & shifted_once(3 downto 1);
shifted_thrice <= '0' & shifted_twice(3 downto 1);
-- If we shifted 4 times... There's cases where the decimal point would cause a carry in to exist!
-- If we don't take that into account... the number 4 will NEVER show up!
-- Here's how to figure out if there can be a carry in
-- 1001 -> 0100,1, so index 0 is when it's shifted once
-- 1100 -> 0001,1 so index 2 is the deecimal when shifted 3 times.
-- If both are true, the addition should've made a carry in!
carry_in <= ADCbin(0) AND ADCbin(2);
-- Both are then added to give the result of the 2/3 multiplication (0.625)
result : Add4Bits port map (
A => shifted_once,
B => shifted_thrice,
C => carry_in,
R => added,
Rc => carry_out
);
-- The functional specifications require an output of 2 downto 0. MSB would never be 1 anyways.
A2_3 <= added(2 downto 0);
end Behavioral;
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