transition : process (currentState, writeEnable, bitCounter)
    begin
        case currentState is
        when IDLE =>
            if writeEnable = '1' then
                nextState <= START_BIT;
            else
                nextState <= IDLE;
            end if;
        when START_BIT =>
            nextState <= DATA_BIT;
        when DATA_BIT =>
            if bitCounter = 0 then
                nextState <= STOP_BIT;
            else
                nextState <= DATA_BIT;
            end if;
        when STOP_BIT =>
            nextState <= IDLE;
        when others =>
            nextState <= IDLE;
        end case;
    end process;

    stateMemory : process (baudClock)
    begin
        if rising_edge(baudClock) then
            if reset='1' then
                currentState <= IDLE;
            else
                currentState <= nextState;
            end if;
        end if;
    end process;

    outputs : process (currentState, bitCounter)
    begin
        case currentState is
        when IDLE =>
            txReady <= '1';
            txData <= '1';
        when START_BIT =>
            txReady <= '0';
            txData <= '0';
        when DATA_BIT =>
            txReady <= '0';
            txData <= txReg(0);
        when STOP_BIT =>
            txReady <= '0';
            txData <= '1';
        end case;
    end process;

    -- shift register
    shiftRegister : process (baudClock, reset)
    begin
        if reset = '1' then
            txReg <= (others => '0');
        elsif rising_edge(baudClock) then
            if currentState = DATA_BIT then
                txReg <= '0' & txReg(7 downto 1);
            else
                txReg <= writeData;
            end if;
        end if;
    end process;

    -- bit counter
    baudCount : process (baudClock, reset)
    begin
        if reset = '1' then
            bitCounter <= 7;
        elsif rising_edge(baudClock) then
            if currentState = DATA_BIT then
                if bitCounter > 0 then
                    bitCounter <= bitCounter - 1;
                else
                    bitCounter <= 0;
                end if;
            else
                bitCounter <= 7;
            end if;
        end if;
    end process;