Uart

Universal Asynchronous Receiver Transmitter Submitted By:- HariomMeena(2009cs10190) Rohan Sharma(2009cs10211) Introduction Universal Asynchronous Receiver Transmitter is a circuit that controls a computer’s interface to its attached devices. It provides the computer interface so that computer can exchange data with devices. The UART takes bytes of data and transmits the individual bits in a sequential fashion. It performs all the tasks (e.g. parity checking etc.) needed for the communication. When transmitting data UART, receives the data parallel from the application, and sends it serially on TxD pin, and when receiving, the UART receives the data serially on RxD pin, and provides the parallel data to the application. Data Encoding When no data transmitted D remains high. To signal a start of new transmission D goes low for 1 bit period, which is known as “Start bit”. After the Start Bit, the individual bits of data are sent. Each bit in the transmission is transmitted for exactly the same amount of time as all of the other bits. After transmission of entire data has been sent then D again goes to high, the last bit known as “Stop bit”. Transmission of next data can begin any time after that. In our project we have “even parity” bit for parity check. UART Data Packet UART Components A UART is composed of three main component receiver, transmitter and baud rate generator 41148005229225TransmitterControl00TransmitterControlUART Block Diagram Inputs: ,[object Object]

RxD: Data coming from PC serial port.

DataSel: Selects whether data to be transmitted is coming from external keyboard attached to fpga or data coming from pc serial port.

External KeyboardOutputs: ,[object Object]

Data Out: Data received is shown on LED’s on fpga. In case parity check fails, then output is always shown as “E”. Top Level Vhdl Code: library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; entity rtot is Port ( clk100mhz,reset1,rxd,data_ready:in std_logic; TxD,transmitted,received:out std_logic; sel:in std_logic_vector(1 downto 0); data_out:out std_logic_vector(7 downto 0); data_in:out std_logic_vector(7 downto 0) ); end rtot; architecture Behavioral of rtot is component scancodereg generic( CLKFREQ : natural := 50_000; -- main clock freq (KHz) PSCLKFREQ : natural := 10 -- keyboard clock freq (KHz) ); port( clk : in std_logic; -- main clock rst : in std_logic; -- reset psClk : in std_logic; -- keyboard clock psData : in std_logic; -- keyboard data asci : out std_logic_vector(7 downto 0); -- key scancode rdy : out std_logic -- true when scancode is ready ); end component; component uart_receiver Port ( clk : in STD_LOGIC; rx:in std_logic; reset : in STD_LOGIC; baud_tick : in STD_LOGIC; data_out : out STD_LOGIC_VECTOR(7 downto 0); received : out STD_LOGIC; count1:out std_logic_vector(3 downto 0); count2:out std_logic_vector(2 downto 0) ); end component; component baud Port ( clk,resetb:in std_logic; counter: out std_logic_vector(7 downto 0):=quot;
00000000quot;
; bclk:out std_logic; sel:in std_logic_vector(1 downto 0) ); end component; component uart_tx port ( clk : in STD_LOGIC; reset : in STD_LOGIC; tx_start : in STD_LOGIC; s_tick : in STD_LOGIC; din : in std_logic_vector ( 7 downto 0); tx_done_tick : out STD_LOGIC; tx : out STD_LOGIC; count1:out std_logic_vector(3 downto 0); count2:out std_logic_vector(2 downto 0) ); end component; signal b:std_logic; signal clkk:std_logic_vector(7 downto 0); signal clk: std_logic:='0'; signal tx:std_logic; signal count1:std_logic_vector(3 downto 0); signal count2:std_logic_vector(2 downto 0); signal count3:std_logic_vector(3 downto 0); signal count4:std_logic_vector(2 downto 0); signal data_out1:std_logic_vector(7 downto 0); begin process(clk100mhz) begin if(clk100mhz'event and clk100mhz='1') -- diving clock t0 50 mhz then clk<=not clk; end if; end process; reset<= not reset1; TxD<=tx; data_out<=data_out1; u1:baud port map(clk,reset,clkk,b,sel); u2:uart_receiver port map(clk,rxd,reset,b,data_out1,received,count1,count2); u5: uart_tx port map (clk,reset,data_ready,b,data_in,transmitted,tx,count3,count4); end Behavioral; Baud Rate Generator The baud rate generator generates a sampling signal whose frequency is exactly 16 times UART’s baud rate. If the baud rate is X, the sampling rate has to be 16*X ticks per second. Assume the system clock rate is 50 MHz the baud generator needs a mod-m (50*106/16*X) counter, in which 1 clock-cycle-tick asserted once every m clock cycle. The baud generator has 2-select bit to decide baud rate, since we are using two bits, we have the choice of four baud rates. Select BAUD Rate 00 9600 01 4800 10 38400 11 19200 VHDL Model library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; entity baud is Port ( clk,resetb:in std_logic; counter: out std_logic_vector(7 downto 0):=quot;
00000000quot;
; bclk:out std_logic ; --baud clock out sel:in std_logic_vector(1 downto 0) ); end baud; architecture Behavioral of baud is signal cnt:std_logic_vector(9 downto 0):=quot;
0000000000quot;
; --to count 163 signal modulus:std_logic_vector(9 downto 0); begin process(sel) begin if(sel=quot;
11quot;
) then modulus<=quot;
0010100010quot;
; --19200 elsif(sel=quot;
10quot;
0001010001quot;
; --38400 elsif(sel=quot;
00quot;
0101000101quot;
; -- 9600 elsif(sel=quot;
01quot;
1010001010quot;
; -- 4800 end if; end process; process(clk,resetb) begin if resetb='1' then cnt<=(others=>'0'); bclk<='0'; elsif rising_edge(clk) then if cnt=modulus then cnt<=(others=>'0'); bclk<='1'; else cnt<=cnt+1; counter<=cnt(7 downto 0); bclk<='0'; end if; end if; end process; end Behavioral; TEST BENCH (BAUD CLOCK) ,[object Object],Here select bits are “11” ,hence baud rate is 19200. Time period of baud clock = 1/(19200* 16)=3.25 *10-6. s ,[object Object],Now select bits are “00” ,hence baud rate =9600 Time period =1/(9600*16) =6.5 * 10-6 s Receiver Receiver takes data serially in RxD pin, and provides the parallel to the Data out pin. UART receiver consists of RDR (Received Data Reg.) and controller. When the UART detects start bit receiver reads and shifts 8 data bits serially into a temporary register. When 8 data bits has been received and parity check passes then after stop bit has been received controller transfers data from temporary register to RDR and received signal goes high. If parity check fails then , output of receiver is always shown as “E”. Receiver state machine Receiver VHDL Model library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; entity uart_receiver is Port ( clk : in STD_LOGIC; rx:in std_logic; reset : in STD_LOGIC; baud_tick : in STD_LOGIC; data_out : out STD_LOGIC_VECTOR(7 downto 0); received : out STD_LOGIC; count1:out std_logic_vector(3 downto 0); count2:out std_logic_vector(2 downto 0) ); end uart_receiver; architecture Behavioral of uart_receiver is type state is (idle,startbit,databits,paritybit,stopbit); signal state_reg,next_state_reg: state; signal counter,next_count:std_logic_vector(3 downto 0); signal data_count,data_next_count:std_logic_vector(2 downto 0); signal rec,next_rec:std_logic_vector(7 downto 0):=quot;
00000000quot;
; signal parity:std_logic; begin process(clk, reset) begin if(reset='1') then state_reg<=idle; counter<=(others=>'0'); data_count<=(others=>'0'); elsif(rising_edge(clk) AND reset='0') then state_reg<=next_state_reg; counter<=next_count; data_count<=data_next_count; rec<=next_rec; end if; end process; state_decode:process (state_reg,rx,counter,baud_tick) begin if(state_reg=idle) then next_state_reg <= state_reg; data_next_count<=data_count; received<='0'; next_count<=counter; next_rec<=rec; if (rx = '0') then next_state_reg <= startbit; next_count<=(others=>'0'); next_rec<=quot;
00000000quot;
; end if; elsif(rising_edge(baud_tick)) then next_state_reg <= state_reg; data_next_count<=data_count; received<='0'; next_count<=counter; next_rec<=rec; if(state_reg= startbit)then if(('0'&counter)=7) then next_state_reg <=databits; next_count<=(others=>'0'); data_next_count<=(others=>'0'); else next_count<=counter+1; end if; elsif(state_reg= databits)then if(('0'&counter)=15) then next_count<=(others=>'0'); next_rec<=(rx & rec( 7 downto 1)); if(('0'&data_count)=7)then next_state_reg<=paritybit; else data_next_count<=data_count+1; end if; else next_count<=counter+1; end if; elsif(state_reg= paritybit)then if(('0'&counter)=15) then next_count<=(others=>'0'); next_state_reg<=stopbit; if(not(parity=rx)) then next_rec<=quot;
01000101quot;
; end if; else next_count<=counter+1; end if; elsif(state_reg= stopbit) then if(('0'&counter)=10) then received<='1'; next_count<=counter+1; elsif(('0'&counter)=15) then next_state_reg <=idle; else next_count<=counter+1; end if; end if; end if; end process; parity<=rec(7) xor rec(6) xor rec(5) xor rec(4) xor rec(3) xor rec(2) xor rec(1) xor rec(0); data_out<=rec; count1<=counter; count2<=data_count; end Behavioral; Transmitter Transmitter takes parallel data and sends it serially on the TxD pin. The transmitter consists of TDR (Transmit Data Register), TSR (Transmit Shift Register) and controller. As load signal goes high transmitter transfers data from TDR to TSR and outputs start bit “0” to the TxD pin then shifts TSR right eight times to transmit 8 bits. When eight data bits transmitted ,transmitter sends parity bit and finally outputs stop bit”1” to the TxD pin and signal “transmitted” goes high. Transmitter VHDL Model library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; entity transmitter is port( clk : in STD_LOGIC; reset : in STD_LOGIC; load : in STD_LOGIC; baud_tick : in STD_LOGIC; din : in std_logic_vector ( 7 downto 0); transmitted : out STD_LOGIC; TxD : out STD_LOGIC; count1:out std_logic_vector(3 downto 0); count2:out std_logic_vector(2 downto 0) ); end transmitter; architecture arch of transmitter is type state is (idle,start,data,parity_s,stop); signal state_reg,state_next:state; signal count,count_next:std_logic_vector (3 downto 0); signal dcount , dcount_next : std_logic_vector ( 2 downto 0); signal TSR , TSR_next : std_logic_vector (7 downto 0):=quot;
00000000quot;
; signal tx ,tx_next : std_logic ; signal parity:std_logic; begin process(clk, reset) begin if(reset='1') then state_reg<=idle; count<=(others=>'0'); dcount<=(others=>'0'); TSR<=(others=>'0'); tx<='1'; elsif(rising_edge(clk) AND reset='0') then state_reg<=state_next; count<=count_next; dcount<=dcount_next; TSR<=TSR_next; tx<=tx_next; end if; end process; state_decode:process (state_reg,baud_tick,tx,load,din) begin if(state_reg=idle) then state_next<=state_reg; count_next<=count; dcount_next<=dcount; TSR_next<=TSR; transmitted<='0'; tx_next<='1'; if (load = '1') then state_next<=start; count_next<=(others=>'0'); TSR_next<=din; end if; elsif(rising_edge(baud_tick)) then state_next<=state_reg; count_next<=count; dcount_next<=dcount; TSR_next<=TSR; tx_next<=tx; transmitted<='0'; if(state_reg= start) then tx_next<=tx; if(('0'&count)=15) then state_next <= data; count_next<=(others=>'0'); dcount_next<=(others=>'0'); else count_next<=count+1; end if; end if; if(state_reg = data) then tx_next<=TSR(0); if(count=15) then count_next <=(others=>'0'); TSR_next <= '0' & TSR(7 downto 1); if(dcount=7) then state_next <= parity_s; else dcount_next<=dcount+1; end if; else count_next <= count + 1; end if; end if; if(state_reg= parity_s) then tx_next<=parity; if(count=15) then count_next <= (others=>'0'); state_next <= stop; else count_next <= count + 1; end if; end if; if(state_reg= stop) then tx_next<='1'; if(count=10) then transmitted<='1'; count_next <= count + 1 elsif(count=15) then state_next <= idle; else count_next <= count + 1; end if; end if; end if; end process; count1 <= (count); count2 <= dcount; parity<=din(7) xor din(6) xor din(5) xor din(4) xor din(3) xor din(2) xor din(1) xor din(0); TxD <= tx; end arch; TestBench(Receiver and Transmitter): ,[object Object],529501515923590047527531741214 ,[object Object], RxD(rx)= START_BIT 1 0 1 0 1 0 1 1 STOP_BIT (Trasmitted) Received data(Data_out)= “11010101” (Data Received) ,[object Object],Trnsmitted data(Data_in)= “10111010” TxD(txbit)= START_BIT 0 1 0 1 1 1 0 1 STOP_BIT 396594411802142)Output of receiver is going to input of transmitter(No Parity Check Here). RxD(rx) = START_BIT 1 0 1 0 1 0 1 1 STOP_BIT(Transmit signal) Trasmit signal is given at around 600 us. TxD(txbit)= START_BIT 1 0 1 0 1 0 1 1 STOP_BIT 3)Output of transmitter is going to input of receiver(No Parity Check Here). 581890914023930046464271631891 Transmitted Data(Data_in) = “1011 1010” (Transmitted) Received Data(Data_out) = “1011 1010” (Received) 4)Parity check(even parity). Here I am sending same data two times , first time with wrong parity , and 2nd time with correct parity. Rxd = START_BIT 0 1 0 1 0 1 1 0 Parity_bit(0) STOP_BIT Hence first time output is h6A (since parity is correct). Ans 2nd time output is h45(“E” since parity bit is wrong ). Work by each member: ,[object Object]

Rohan Sharma: Receiver, Baud Generator, External Keyboard drivers.

Uart

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