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Tiny Serial TX

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I've been beavering away on a large project, but ended up thinking about how small a Serial TX module could be. While out splitting firewood stumbled over the idea that takes it down top 12 LUTs and 11 flip-flopsĀ 

library IEEE;

entity tiny_rs232_tx is
    Port ( clk         : in  STD_LOGIC;
           bit_tick    : in  STD_LOGIC;
           data        : in  STD_LOGIC_VECTOR(7 downto 0);
           data_enable : in  STD_LOGIC;
           tx          : out STD_LOGIC := '1';
           busy        : out STD_LOGIC );
end tiny_rs232_tx;

architecture Behavioral of tiny_rs232_tx is
    signal shift_reg  : std_logic_vector(9 downto 0) := (others => '1');
    signal i_busy     : std_logic;
    busy <= i_busy;
    with shift_reg select i_busy <= '0' when "0000000000", '1' when others;

clk_proc: process(clk)
        if rising_edge(clk) then
            if i_busy = '0' and data_enable = '1' then
                shift_reg <= '1' & data & '0';
            end if;             
            if bit_tick = '1' then
                if i_busy = '1' then
                    tx <= shift_reg(0);
                    shift_reg <= '0' & shift_reg(9 downto 1);
                end if;
            end if;
        end if;
    end process;
end Behavioral;
Edited by hamster

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