Subversion Repositories uart_block

--! Data transmitter

--! http://www.fpga4fun.com/SerialInterface.html

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

--! Use CPU Definitions package

use work.pkgDefinitions.all;

entity serial_transmitter is

    Port ( rst : in  STD_LOGIC;

           baudClk : in  STD_LOGIC;

           data_byte : in  STD_LOGIC_VECTOR ((nBits-1) downto 0);

                          data_sent : out STD_LOGIC;

           serial_out : out  STD_LOGIC);

end serial_transmitter;

architecture Behavioral of serial_transmitter is

signal current_s,next_s: txStates;

begin

        -- Next state process

        process (rst, baudClk)

        begin

                if rst = '1' then

                        current_s <= tx_idle;

                elsif rising_edge(baudClk) then

                        current_s <= next_s;

                end if;

        end process;

        process (current_s, data_byte)

        begin

                case current_s is

                        when tx_idle =>

                                serial_out <= '1';

                                data_sent <= '0';

                                next_s <= tx_start;

                        -- Start bit

                        when tx_start =>

                                serial_out <= '0';

                                data_sent <= '0';

                                next_s <= bit0;

                        when bit0 =>    -- Send the least significat bit

                                serial_out <= data_byte(0);

                                data_sent <= '0';

                                next_s <= bit1;

                        when bit1 =>

                                serial_out <= data_byte(1);

                                data_sent <= '0';

                                next_s <= bit2;

                        when bit2 =>

                                serial_out <= data_byte(2);

                                data_sent <= '0';

                                next_s <= bit3;

                        when bit3 =>

                                serial_out <= data_byte(3);

                                data_sent <= '0';

                                next_s <= bit4;

                        when bit4 =>

                                serial_out <= data_byte(4);

                                data_sent <= '0';

                                next_s <= bit5;

                        when bit5 =>

                                serial_out <= data_byte(5);

                                data_sent <= '0';

                                next_s <= bit6;

                        when bit6 =>

                                serial_out <= data_byte(6);

                                data_sent <= '0';

                                next_s <= bit7;

                        when bit7 =>    -- Send the most significat bit

                                serial_out <= data_byte(7);

                                data_sent <= '0';

                                next_s <= tx_stop1;

                        when tx_stop1 =>

                                serial_out <= '1';

                                data_sent <= '1';

                                next_s <= tx_stop2;

                        when tx_stop2 =>        -- Stop here and wait for other reset

                                serial_out <= '1';

                                data_sent <= '1';

                                next_s <= tx_stop2;

                end case;

        end process;

end Behavioral;