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<P><table class="ttop"><th class="tpre"><a href="26_Listing_of_uart_rx.vhd.html">Previous Lesson</a></th><th class="ttop"><a href="toc.html">Table of Content</a></th><th class="tnxt"><a href="28_Listing_of_RAMB4_S4_S4.vhd.html">Next Lesson</a></th></table>
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<H1><A NAME="section_1">27 LISTING OF uart_tx.vhd</A></H1>
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<pre class="vhdl">
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  1     -------------------------------------------------------------------------------
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  2     --
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  3     -- Copyright (C) 2009, 2010 Dr. Juergen Sauermann
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  4     --
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  5     --  This code is free software: you can redistribute it and/or modify
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  6     --  it under the terms of the GNU General Public License as published by
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  7     --  the Free Software Foundation, either version 3 of the License, or
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  8     --  (at your option) any later version.
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  9     --
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 10     --  This code is distributed in the hope that it will be useful,
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 11     --  but WITHOUT ANY WARRANTY; without even the implied warranty of
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 12     --  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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 13     --  GNU General Public License for more details.
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 14     --
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 15     --  You should have received a copy of the GNU General Public License
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 16     --  along with this code (see the file named COPYING).
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 17     --  If not, see http://www.gnu.org/licenses/.
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 18     --
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 19     -------------------------------------------------------------------------------
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 20     -------------------------------------------------------------------------------
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 21     --
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 22     -- Module Name:    uart_tx - Behavioral
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 23     -- Create Date:    14:21:59 11/07/2009
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 24     -- Description:    a UART receiver.
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 25     --
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 26     -------------------------------------------------------------------------------
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 27     --
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 28     library IEEE;
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 29     use IEEE.STD_LOGIC_1164.ALL;
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 30     use IEEE.STD_LOGIC_ARITH.ALL;
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 31     use IEEE.STD_LOGIC_UNSIGNED.ALL;
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 32
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 33     entity uart_tx is
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 34         port(   I_CLK       : in  std_logic;
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 35                 I_CLR       : in  std_logic;            -- RESET
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 36                 I_CE_1      : in  std_logic;            -- BAUD rate clock enable
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 37                 I_DATA      : in  std_logic_vector(7 downto 0);   -- DATA to be sent
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 38                 I_FLAG      : in  std_logic;            -- toggle to send data
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 39                 Q_TX        : out std_logic;            -- Serial output line
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 40                 Q_FLAG      : out std_logic);           -- Transmitting Flag
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 41     end uart_tx;
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 42
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 43     architecture Behavioral of uart_tx is
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 44
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 45     signal L_BUF            : std_logic_vector(7 downto 0);
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 46     signal L_TODO           : std_logic_vector(3 downto 0);     -- bits to send
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 47     signal L_FLAG           : std_logic;
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 48
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 49     begin
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 51         process(I_CLK)
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 52         begin
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 53             if (rising_edge(I_CLK)) then
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 54                 if (I_CLR = '1') then
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 55                     Q_TX   <= '1';
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 56                     L_BUF  <= "11111111";
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 57                     L_TODO <= "0000";
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 58                     L_FLAG <= I_FLAG;                   -- idle
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 59                 elsif (I_CE_1 = '1') then
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 60                     if (L_TODO /= "0000") then          -- transmitting
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 61                         Q_TX <= L_BUF(0);               -- next bit
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 62                         L_BUF     <= '1' & L_BUF(7 downto 1);
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 63                         if (L_TODO = "0001") then
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 64                             L_FLAG <= I_FLAG;
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 65                         end if;
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 66                         L_TODO <= L_TODO - "0001";
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 67                     elsif (L_FLAG /= I_FLAG) then       -- new byte
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 68                         Q_TX <= '0';                    -- start bit
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 69                         L_BUF <= I_DATA;                -- data bits
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 70                         L_TODO <= "1001";
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 71                     end if;
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 72                 end if;
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 73             end if;
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 74         end process;
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 75
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 76         Q_FLAG <= L_FLAG;
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 77
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 78     end Behavioral;
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 79
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<pre class="filename">
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src/uart_tx.vhd
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</pre></pre>
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<P>
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<P><hr><BR>
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<table class="ttop"><th class="tpre"><a href="26_Listing_of_uart_rx.vhd.html">Previous Lesson</a></th><th class="ttop"><a href="toc.html">Table of Content</a></th><th class="tnxt"><a href="28_Listing_of_RAMB4_S4_S4.vhd.html">Next Lesson</a></th></table>
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