Subversion Repositories uart2bus

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-- baud rate generator for uart 

--

-- this module has been changed to receive the baud rate dividing counter from registers.

-- the two registers should be calculated as follows:

-- first register:

--              baud_freq = 16*baud_rate / gcd(global_clock_freq, 16*baud_rate)

-- second register:

--              baud_limit = (global_clock_freq / gcd(global_clock_freq, 16*baud_rate)) - baud_freq 

--

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library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity baudGen is

  port ( clr       : in  std_logic;                     -- global reset input

         clk       : in  std_logic;                     -- global clock input

         -- baudFreq = 16 * baudRate / gcd(clkFreq, 16 * baudRate)

         baudFreq  : in  std_logic_vector(11 downto 0); -- baud rate setting registers - see header description

         -- baudLimit = clkFreq / gcd(clkFreq, 16 * baudRate) - baudFreq

         baudLimit : in  std_logic_vector(15 downto 0); -- baud rate setting registers - see header description

         ce16      : out std_logic);                    -- baud rate multiplyed by 16

end baudGen;

architecture Behavioral of baudGen is

  signal counter : std_logic_vector(15 downto 0);

  begin

    -- baud divider counter

    -- clock divider output

    process (clr, clk)

    begin

      if (clr = '1') then

        counter <= (others => '0');

        ce16 <= '0';

      elsif (rising_edge(clk)) then

        if (counter >= baudLimit) then

          counter <= counter - baudLimit;

          ce16 <= '1';

        else

          counter <= counter + baudFreq;

          ce16 <= '0';

        end if;

      end if;

    end process;

  end Behavioral;