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Hello, I am trying to send a character to FPGA from PC hyper terminal , for eg : 's' to start other processes in FPGA like initiating generation of CCD signals and sampling ADC et al and a different ascii character to stop the processes. I am able to send a ASCII character from PC hyper terminal and receive binary value it on FPGA LED's however I'm unable to use this for control. Please find my top level code below. 'Start' signal is to be controlling the initiation of other processes. library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.NUMERIC_STD.ALL; Library UNISIM; use UNISIM.vcomponents.all; Library UNIMACRO; use UNIMACRO.vcomponents.all; use IEEE.MATH_REAL.ALL; ----------------------------------------------------- entity top_module is port( --------------------UART_GUI------------------------------- RxD : IN STD_LOGIC; RxData : INOUT STD_LOGIC_VECTOR(7 DOWNTO 0); ---COMMON INPUTS--- clk, rst : in std_logic; --send_ccd : in std_logic;---------------CCD control SH,ICG,master_ccd_clock : out std_logic; ----FOR AD7980-------- --sample: in std_logic; -------------- to start sampling samp_ind: out std_logic;---------------indicates sampling in process adc_cnv : out std_logic;---------------cnv for AD7980 adc_clk : inout std_logic;--------------SPI clock adc_miso : in std_logic;------------------output from AD7980 -------FIFO SIGNALS-------- WriteEn , ReadEn : in std_logic; -------------fifo controls full, empty : out std_logic ------------------indicates fifo status ); end top_module; architecture structural of top_module is ----------------------------------------------------------------------------UART CONTROL GUI------------------------------------- component receiver IS PORT ( clk : IN STD_LOGIC; reset : IN STD_LOGIC; RxD : IN STD_LOGIC; RxData : INOUT STD_LOGIC_VECTOR(7 DOWNTO 0) ); END component receiver; ----------------------------------------FIFO COMPONENT DECLARATION ----------------------------------------------------------------- component fifo is port ( reset_rtl_0 : in STD_LOGIC; clk_100MHz : in STD_LOGIC; full_0 : out STD_LOGIC; din_0 : in STD_LOGIC_VECTOR ( 15 downto 0 ); wr_en_0 : in STD_LOGIC; empty_0 : out STD_LOGIC; dout_0 : out STD_LOGIC_VECTOR ( 15 downto 0 ); rd_en_0 : in STD_LOGIC ); end component fifo; -------------------------------------------------------------------------------------------------------------------------- signal fifo_data_out : STD_LOGIC_VECTOR (15 downto 0); signal adc_out : std_logic_vector(15 downto 0); signal start :std_logic; -------------------------UART_RX_FOR CONTROL_ OF_PROCESSES--------------------------------------------------------------- process(Clk,RxData) begin if RxData = "01110011" then start <= '1' ; elsif RxData = "01110000" then start <= '0'; else start <= '0'; end if; end process; --------------------AD7980PORTMAP---------------------------------------------------------------------------------- AD7980 : entity work.AD7980 port map ( clock => clk, sample => start, -- data output Dout => adc_out(15 downto 0), samp_ind => samp_ind, -- ADC connection adc_miso => adc_miso, adc_cnv => adc_cnv, adc_clk =>adc_clk ); ---------------------------------------------FIFO PORTMAP---------------------------------------------------------------- fifo_i: component fifo port map ( clk_100MHz => clk, din_0(15 downto 0) => adc_out(15 downto 0), dout_0(15 downto 0) => fifo_data_out(15 downto 0), empty_0 => empty, full_0 => full, rd_en_0 => ReadEn, reset_rtl_0 => rst, wr_en_0 => WriteEn ); ccd_control : entity work.TCD1103GFG port map ( clock => clk, send => start, SH => SH, ICG => ICG, master_ccd_clock => master_ccd_clock); ---------------------------------------------------------------UART GUI CONTROL--------------------------------------- uart_gui : entity work.receiver port map ( clk => clk, reset => rst, RxD => RxD, RxData => RxData ); end structural; Here is the UART receiver open source code I'm using that works LIBRARY ieee; USE ieee.std_logic_1164.all; USE ieee.std_logic_unsigned.all; use ieee.std_logic_arith.all; ENTITY receiver IS PORT ( clk : IN STD_LOGIC; reset : IN STD_LOGIC; RxD : IN STD_LOGIC; RxData : INOUT STD_LOGIC_VECTOR(7 DOWNTO 0) ); END receiver; ARCHITECTURE behavioural OF receiver IS SIGNAL shift : STD_LOGIC; SIGNAL state : STD_LOGIC; SIGNAL nextstate : STD_LOGIC; SIGNAL bitcounter : STD_LOGIC_VECTOR(3 DOWNTO 0); SIGNAL samplecounter : STD_LOGIC_VECTOR(1 DOWNTO 0); SIGNAL counter : STD_LOGIC_VECTOR(13 DOWNTO 0); SIGNAL rxshiftreg : STD_LOGIC_VECTOR(9 DOWNTO 0); SIGNAL clear_bitcounter : STD_LOGIC; SIGNAL inc_bitcounter : STD_LOGIC; SIGNAL inc_samplecounter : STD_LOGIC; SIGNAL clear_samplecounter : STD_LOGIC; constant clk_freq: integer := 100000000; constant baud_rate :integer := 9600; constant div_sample :integer := 4; constant div_counter :integer := (clk_freq/(baud_rate*div_sample)); constant mid_sample : integer := (div_sample/2); constant div_bit : integer := 10; BEGIN RxData <= rxshiftreg(8 DOWNTO 1); PROCESS (clk) BEGIN IF (clk'EVENT AND clk = '1') THEN IF (reset = '1') THEN state <= '0'; bitcounter <= "0000"; counter <= "00000000000000"; samplecounter <= "00"; ELSE counter <= counter + "00000000000001"; if (counter>= div_counter - 1) then counter <= "00000000000000"; state <= nextstate; IF (shift = '1') THEN rxshiftreg <= (RxD & rxshiftreg(9 DOWNTO 1)); END IF; IF (clear_samplecounter = '1') THEN samplecounter <= "00"; END IF; IF (inc_samplecounter = '1') THEN samplecounter <= samplecounter + "01"; END IF; IF (clear_bitcounter = '1') THEN bitcounter <= "0000"; END IF; IF (inc_bitcounter = '1') THEN bitcounter <= bitcounter + "0001"; END IF; END IF; END IF; END IF; END PROCESS; PROCESS (clk) BEGIN IF (clk'EVENT AND clk = '1') THEN shift <= '0'; clear_samplecounter <= '0'; inc_samplecounter <= '0'; clear_bitcounter <= '0'; inc_bitcounter <= '0'; nextstate <= '0'; CASE state IS WHEN '0' => IF (RxD = '1') THEN nextstate <= '0'; ELSE nextstate <= '1'; clear_bitcounter <= '1'; clear_samplecounter <= '1'; END IF; WHEN '1' => nextstate <= '1'; IF (samplecounter = (mid_sample - 1)) THEN shift <= '1'; END IF; IF (samplecounter = (div_sample - 1)) THEN IF (bitcounter = (div_bit - 1)) THEN nextstate <= '0'; END IF; inc_bitcounter <= '1'; clear_samplecounter <= '1'; ELSE inc_samplecounter <= '1'; END IF; WHEN OTHERS => nextstate <= '0'; END CASE; END IF; END PROCESS; end behavioural; I'm unsure if the issue is because of the number of clock cycles for which the character 's' exists. Please help me understand the miss here.