Subversion Repositories manchesterencoderdecoder

 
library ieee ;
use ieee.std_logic_1164.all ;
use ieee.std_logic_arith.all ;
 
entity me is
port (
       rst : in std_logic;  -- Power On Reset Active High
       rts : in std_logic;  -- Request To Send Active Low
       txd : in std_logic; -- Data To Be Transmitted
       clkin : in std_logic ; -- Clk Input
       cts : out std_logic ;  -- Clear to Sen Output Active Low
       txcout : out std_logic;  -- TX CLK = just clkin /16
       txlen : out std_logic;  -- TX Enable Active High
       mdo   : out std_logic -- Manchester Encoded Data Output (TX "01" for 1 and "10" for 0)
) ;
end me ;
 
-------------------------------------------------------------------------------
architecture rtl of me is
-------------------------------------------------------------------------------
 
-------------------------------------------------------------------------------
begin -- architecture rtl
-------------------------------------------------------------------------------
 
-------------------------------------------------------------------------------
 main : process (rst, clkin)
-------------------------------------------------------------------------------
   type state_t is (
     idle,
     preamble,
     postpreamble,
     sending,
     eom
   );
   variable state : state_t;
   variable PrCounter : integer range 0 to 31;
   variable TxCounter : integer range 0 to 15;
   -- variables to hold the internal value of the output ports:
   variable TXCOUT_i : std_logic;
   variable CTS_i    : std_logic;
   variable MDO_i    : std_logic;
   variable MDO_i1    : std_logic;
   variable TXLEN_i  : std_logic;
-------------------------------------------------------------------------------
 begin
-------------------------------------------------------------------------------
   if rst='1' then
-------------------------------------------------------------------------------
     --asynchronously reset all internal variables
     state     := idle;
     PrCounter :=  30 ; -- adjunt to length of your preamble
     TxCounter :=  0 ;
     TXCOUT_i  := '0';
     CTS_i     := '1';
     MDO_i     := '0';
     MDO_i1     := '0';
     TXLEN_i   := '0';
-------------------------------------------------------------------------------
   elsif clkin'event and clkin='1' then
-------------------------------------------------------------------------------
     --counter for clkin/16
     --must txcout have a 50% duty cycle?
     TxCounter := (TxCounter + 1) mod 16;
     if TxCounter = 0 then
       TXCOUT_i := '0';
     end if;
     if TxCounter = 8 then
       TXCOUT_i := '1';
     end if;
-------------------------------------------------------------------------------
     case state is
-------------------------------------------------------------------------------
       when idle =>
         if rts = '0' then
           state := preamble;
           PrCounter :=  30 ;
           MDO_i := '0';
         end if;
-------------------------------------------------------------------------------
       when preamble =>
 
         if TxCounter = 8 then  --when to mark?  2? 3? ..7? 8?
           TXLEN_i := '1';      --when will it be turned off ?  never?
         end if;
         if TxCounter = 8 then  --when to toggle? 2? 3? .. 6?
 
           MDO_i := not(MDO_i); --preamble 15 times '10'
 
           PrCounter := PrCounter - 1;
           if PrCounter = 0 then
              state := postpreamble;
              PrCounter := 2; -- adjunt to length of your post-preamble.
           end if;
 
         end if;
 
-------------------------------------------------------------------------------
       when postpreamble =>
         if TxCounter = 8 then  --when to toggle? 2? 3? .. 6?
           MDO_i := '1';        -- post preamble: '11'
           PrCounter := PrCounter - 1;
           if PrCounter = 0 then
              --MDO_i := txd;
              state := sending;
              CTS_i := '0';      --when will it be turned off ?  never? 
           end if;
         end if;
 
-------------------------------------------------------------------------------
       when sending =>
         if TxCounter = 8 then
           --this samples the date with clkin, not with txcout..
           --what is actually needed ?
           MDO_i := txd;
           if (rts = '1') then
           	state := eom;
           	PrCounter := 2;
           	CTS_i := '1';
           	MDO_i := '1';
           	end if;
 
 
         end if;
 
        when eom =>
 
        if TxCounter = 8 then
        	MDO_i := '1';
        	PrCounter := PrCounter - 1;
        	if PrCounter = 0 then
 
        		state := idle;
        	end if;
 
 
        end if;
 
 
       --manchester encoding not yet implemented, too many open questions..
       --to many unspecified specifications ;)!
 
       --how to return to idle?
 
-------------------------------------------------------------------------------
       when others =>
 
       state := idle;
-------------------------------------------------------------------------------
 
-------------------------------------------------------------------------------
     end case;
 
     if state /= idle then
 
       if state = eom then
       	 MDO_i1 := MDO_i;
 
       elsif TxCounter = 8 then
 
 	  TXLEN_i := '1';
 	  MDO_i1 := not MDO_i;
       elsif TxCounter = 0 then
 
   	  MDO_i1 := MDO_i;
       end if;
      elsif TXCounter = 8 then
      	TXLEN_i := '0';
     end if;
-------------------------------------------------------------------------------
 
-------------------------------------------------------------------------------
   end if;
-------------------------------------------------------------------------------
   --assign output ports:
   txcout <= TXCOUT_i;
   cts    <= CTS_i;
   mdo    <= MDO_i1;
   txlen  <= TXLEN_i;
-------------------------------------------------------------------------------
 end process main;
-------------------------------------------------------------------------------
 
-------------------------------------------------------------------------------
end ; -- architecture rtl
------------------------------------------
-- ME2.vhd