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Uart TX - VHD

The document describes a VHDL implementation of a UART transmitter (uart_tx) designed by engineer Joash Naidoo. It includes ports for clock, reset, data input, enable signal, busy output, and transmission output, along with a behavioral architecture that manages the transmission of data bits. The design features a counter for clock cycles per bit and logic to handle the start, data, and stop bits during transmission.

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8 views2 pages

Uart TX - VHD

The document describes a VHDL implementation of a UART transmitter (uart_tx) designed by engineer Joash Naidoo. It includes ports for clock, reset, data input, enable signal, busy output, and transmission output, along with a behavioral architecture that manages the transmission of data bits. The design features a counter for clock cycles per bit and logic to handle the start, data, and stop bits during transmission.

Uploaded by

pahlevanmansour9
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as TXT, PDF, TXT or read online on Scribd
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----------------------------------------------------------------------------------

-- Company:
-- Engineer: Joash Naidoo
----------------------------------------------------------------------------------

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity uart_tx is
Port ( clk : in STD_LOGIC;
reset : in STD_LOGIC;
data_in : in STD_LOGIC_VECTOR(7 downto 0);
en : in STD_LOGIC;
busy_out : out STD_LOGIC;
tx_out : out STD_LOGIC
);
end uart_tx;

architecture Behavioral of uart_tx is

constant clks_per_bit : integer := 10417; -- 100 MHz / 9600 baud = 10417

signal cnt : integer range 0 to clks_per_bit-1 := 0;


signal busy : STD_LOGIC := '1'; -- For stability ?
signal bitcnt : STD_LOGIC_VECTOR(3 downto 0) := (others => '0');
signal en_old : STD_LOGIC := '0';

begin

busy_out <= busy;

process(clk) begin
if rising_edge(clk) then

-- Logic
if busy = '0' then
if en = '1' then
-- Begin transaction
cnt <= clks_per_bit-1; -- Hold value for whole period
en_old <= '1';
busy <= '1';
tx_out <= '0';
bitcnt <= X"0";
else
tx_out <= '1';
end if;

else -- Busy=1. Continuing transaction

if bitcnt = 0 then -- Keep transmitting start bit


tx_out <= '0';
elsif bitcnt >= 1 and bitcnt < 9 then -- Transmit corresponding data bit
tx_out <= data_in(conv_integer(bitcnt)-1);
else -- End of transmission
tx_out <= '1';
end if;
if cnt = 0 then -- Only if ready to change to the next bit, change index
if bitcnt < 9 then -- Still have bits to transmit
bitcnt <= bitcnt + 1;
if bitcnt < 8 then
cnt <= clks_per_bit-1; -- Reset the counter
else
cnt <= clks_per_bit-100; -- Reset the counter
end if;
else -- No more bits to transmit
busy <= '0';
bitcnt <= X"0";
end if;

else
cnt <= cnt - 1;
end if;

end if;

end if;
end process;

end Behavioral;

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