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--===========================================================================--

--

--  S Y N T H E Z I A B L E    miniUART   C O R E

--

--  www.OpenCores.Org - January 2000

--  This core adheres to the GNU public license  

--

-- Design units   : miniUART core for the OCRP-1

--

-- File name      : miniuart.vhd

--

-- Purpose        : Implements an miniUART device for communication purposes 

--                  between the OR1K processor and the Host computer through

--                  an RS-232 communication protocol.

--                  

-- Library        : uart_lib.vhd

--

-- Dependencies   : IEEE.Std_Logic_1164

--

-- Simulator      : ModelSim PE/PLUS version 4.7b on a Windows95 PC

--===========================================================================--

-------------------------------------------------------------------------------

-- Revision list

-- Version   Author                 Date           Changes

--

-- 0.1      Ovidiu Lupas     15 January 2000       New model

-- 1.0      Ovidiu Lupas     January  2000         Synthesis optimizations

-- 2.0      Ovidiu Lupas     April    2000         Bugs removed - RSBusCtrl

--          the RSBusCtrl did not process all possible situations

--

--        olupas@opencores.org

--

-- 3.0      John Kent        October  2002         Changed Status bits to match mc6805

--          Added CTS, RTS, Baud rate control & Software Reset

-------------------------------------------------------------------------------

-- Entity for miniUART Unit - 9600 baudrate                                  --

-------------------------------------------------------------------------------

library ieee;

   use ieee.std_logic_1164.all;

   use ieee.numeric_std.all;

entity miniUART is

  port (

     SysClk   : in  Std_Logic;  -- System Clock

     rst      : in  Std_Logic;  -- Reset input (active high)

     cs       : in  Std_Logic;

     rw       : in  Std_Logic;

     RxD      : in  Std_Logic;

     TxD      : out Std_Logic;

     CTS_n    : in  Std_Logic;

     RTS_n    : out Std_Logic;

     Irq      : out Std_Logic;  -- interrupt

     Addr     : in  Std_Logic;  -- Register Select

     DataIn   : in  Std_Logic_Vector(7 downto 0); -- 

     DataOut  : out Std_Logic_Vector(7 downto 0)); -- 

end entity; --================== End of entity ==============================--

-------------------------------------------------------------------------------

-- Architecture for miniUART Controller Unit

-------------------------------------------------------------------------------

architecture uart of miniUART is

  -----------------------------------------------------------------------------

  -- Signals

  -----------------------------------------------------------------------------

  signal RxData : Std_Logic_Vector(7 downto 0); -- 

  signal TxData : Std_Logic_Vector(7 downto 0); -- 

  signal StatReg : Std_Logic_Vector(7 downto 0); -- status register

  signal CtrlReg : Std_Logic_Vector(7 downto 0); -- control register

  --             StatReg detailed 

  -----------+--------+--------+--------+--------+--------+--------+--------+

  --  Int    | PErr   | ORErr  | FErr   | CTS    | DCD    | TBufE  | DRdy   |

  -----------+--------+--------+--------+--------+--------+--------+--------+

  signal EnabRx : Std_Logic;  -- Enable RX unit

  signal EnabTx : Std_Logic;  -- Enable TX unit

  signal DRdy   : Std_Logic;  -- Receive Data ready

  signal TBufE  : Std_Logic;  -- Transmit buffer empty

  signal FErr   : Std_Logic;  -- Frame error

  signal OErr   : Std_Logic;  -- Output error

  signal Read   : Std_Logic;  -- Read receive buffer

  signal Load   : Std_Logic;  -- Load transmit buffer

  signal Int    : Std_Logic;  -- Interrupt bit

  signal Reset  : Std_Logic;  -- Reset (Software & Hardware)

  -----------------------------------------------------------------------------

  -- Baud rate Generator

  -----------------------------------------------------------------------------

  component ClkUnit is

   port (

     Clk      : in  Std_Logic;  -- System Clock

     Reset    : in  Std_Logic;  -- Reset input

     EnableRX : out Std_Logic;  -- Control signal

     EnableTX : out Std_Logic;  -- Control signal

          BaudRate : in  Std_Logic_Vector(1 downto 0));

  end component;

  -----------------------------------------------------------------------------

  -- Receive Unit

  -----------------------------------------------------------------------------

  component RxUnit is

  port (

     Clk    : in  Std_Logic;  -- Clock signal

     Reset  : in  Std_Logic;  -- Reset input

     Enable : in  Std_Logic;  -- Enable input

     RxD    : in  Std_Logic;  -- RS-232 data input

     ReadD  : in  Std_Logic;  -- Read data signal

     FRErr  : out Std_Logic;  -- Status signal

     ORErr  : out Std_Logic;  -- Status signal

     DARdy  : out Std_Logic;  -- Status signal

     DataI  : out Std_Logic_Vector(7 downto 0));

  end component;

  -----------------------------------------------------------------------------

  -- Transmitter Unit

  -----------------------------------------------------------------------------

  component TxUnit is

  port (

     Clk    : in  Std_Logic;  -- Clock signal

     Reset  : in  Std_Logic;  -- Reset input

     Enable : in  Std_Logic;  -- Enable input

     LoadD  : in  Std_Logic;  -- Load transmit data

     TxD    : out Std_Logic;  -- RS-232 data output

     TBE    : out Std_Logic;  -- Tx buffer empty

     DataO  : in  Std_Logic_Vector(7 downto 0));

  end component;

begin

  -----------------------------------------------------------------------------

  -- Instantiation of internal components

  -----------------------------------------------------------------------------

  ClkDiv  : ClkUnit port map (

                Clk      => SysClk,

                                         EnableRx => EnabRX,

                                         EnableTx => EnabTX,

                                         BaudRate => CtrlReg(1 downto 0),

                                         Reset    => Reset);

  TxDev   : TxUnit  port map (

                Clk      => SysClk,

                                         Reset    => Reset,

                                         Enable   => EnabTX,

                                         LoadD    => Load,

                                         TxD      => TxD,

                                         TBE      => TBufE,

                                         DataO    => TxData);

  RxDev   : RxUnit  port map (

                Clk      => SysClk,

                                         Reset    => Reset,

                                         Enable   => EnabRX,

                                         RxD      => RxD,

                                         ReadD    => Read,

                                         FRErr    => FErr,

                                         ORErr    => OErr,

                                         DARdy    => DRdy,

                                         DataI    => RxData);

  -----------------------------------------------------------------------------

  -- Implements the controller for Rx&Tx units

  -----------------------------------------------------------------------------

  RSBusCtrl : process(SysClk, Reset, DRdy, TBufE, FErr, OErr, Int, CtrlReg)

     variable StatM : Std_Logic_Vector(7 downto 0);

  begin

     if SysClk'event and SysClk='0' then

        if Reset = '1' then

           StatM := "00000000";

           Int <= '0';

        else

           StatM(0) := DRdy;

           StatM(1) := TBufE;

                          StatM(2) := '0'; -- DCD

                          StatM(3) := CTS_n;

           StatM(4) := FErr;

           StatM(5) := OErr;

           StatM(6) := '0'; -- Parrity error

                     StatM(7) := Int;

                     Int <= (CtrlReg(7) and DRdy) or

                           ((not CtrlReg(6)) and CtrlReg(5) and TBufE);

        end if;

                 RTS_n <= CtrlReg(6) and not CtrlReg(5);

       Irq <= Int;

       StatReg <= StatM;

     end if;

  end process;

-----------------------------------------------------------------------------

-- Combinational section

-----------------------------------------------------------------------------

control_strobe:  process(SysClk, Reset, cs, rw, Addr, DataIn, CtrlReg )

  begin

   if SysClk'event and SysClk='1' then

          if (reset = '1') then

            CtrlReg <= "00000000";

                 Load <= '0';

                 Read <= '0';

          else

            if cs = '1' then

              if Addr = '1' then

                     CtrlReg <= CtrlReg;

                     if rw = '0' then  -- write data register

                  Load <= '1';

                       Read <= '0';

                else               -- read Data Register

                  Load <= '0';

             Read <= '1';

                          end if; -- rw

              else                 -- read Status Register

                Load <= '0';

                     Read <= '0';

                     if rw = '0' then  -- write data register

                            CtrlReg <= DataIn;

                else               -- read Data Register

                       CtrlReg <= CtrlReg;

                          end if; -- rw

                   end if; -- Addr

            else                   -- not selected

              Load <= '0';

                   Read <= '0';

                        CtrlReg <= CtrlReg;

            end if;  -- cs

          end if; -- reset

   end if; -- SysClk

end process;

---------------------------------------------------------------

--

-- set data output mux

--

--------------------------------------------------------------

data_port: process(Addr, StatReg, RxData, DataIn )

begin

     TxData <= DataIn;

          if Addr = '1' then

                 DataOut <= RxData;  -- read data register

          else

                 DataOut <= StatReg;   -- read status register

          end if; -- Addr

end process;

---------------------------------------------------------------

--

-- reset may be hardware or software

--

---------------------------------------------------------------

uart_reset: process(CtrlReg, rst )

begin

          Reset <= (CtrlReg(1) and CtrlReg(0)) or rst;

end process;

end uart; --===================== End of architecture =======================--