URL https://opencores.org/ocsvn/t65/t65/trunk

Subversion Repositories t65

[/] [t65/] [trunk/] [rtl/] [vhdl/] [T16450.vhd] - Blame information for rev 3

Go to most recent revision | Details | Compare with Previous | View Log


--
-- 16450 compatible UART with synchronous bus interface
-- RClk/BaudOut is XIn enable instead of actual clock
-- No break detection, no modem status change detection
-- Only one stop bit supported
--
-- Version : 0208
--
-- Copyright (c) 2002 Daniel Wallner (jesus@opencores.org)
--
-- All rights reserved
--
-- Redistribution and use in source and synthezised forms, with or without
-- modification, are permitted provided that the following conditions are met:
--
-- Redistributions of source code must retain the above copyright notice,
-- this list of conditions and the following disclaimer.
--
-- Redistributions in synthesized form must reproduce the above copyright
-- notice, this list of conditions and the following disclaimer in the
-- documentation and/or other materials provided with the distribution.
--
-- Neither the name of the author nor the names of other contributors may
-- be used to endorse or promote products derived from this software without
-- specific prior written permission.
--
-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-- AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
-- THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
-- PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE
-- LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
-- CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-- SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-- INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
-- CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-- ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-- POSSIBILITY OF SUCH DAMAGE.
--
-- Please report bugs to the author, but before you do so, please
-- make sure that this is not a derivative work and that
-- you have the latest version of this file.
--
-- The latest version of this file can be found at:
--      http://www.opencores.org/cvsweb.shtml/t80/
--
-- Limitations :
--
-- File history :
--
 
library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.numeric_std.all;
 
entity T16450 is
        port(
                MR_n            : in std_logic;
                XIn                     : in std_logic;
                RClk            : in std_logic;
                CS_n            : in std_logic;
                Rd_n            : in std_logic;
                Wr_n            : in std_logic;
                A                       : in std_logic_vector(2 downto 0);
                D_In            : in std_logic_vector(7 downto 0);
                D_Out           : out std_logic_vector(7 downto 0);
                SIn                     : in std_logic;
                CTS_n           : in std_logic;
                DSR_n           : in std_logic;
                RI_n            : in std_logic;
                DCD_n           : in std_logic;
                SOut            : out std_logic;
                RTS_n           : out std_logic;
                DTR_n           : out std_logic;
                OUT1_n          : out std_logic;
                OUT2_n          : out std_logic;
                BaudOut         : out std_logic;
                Intr            : out std_logic
        );
end T16450;
 
architecture rtl of T16450 is
 
        signal  RBR                             : std_logic_vector(7 downto 0);  -- Reciever Buffer Register
        signal  THR                             : std_logic_vector(7 downto 0);  -- Transmitter Holding Register
        signal  IER                             : std_logic_vector(7 downto 0);  -- Interrupt Enable Register
        signal  IIR                             : std_logic_vector(7 downto 0);  -- Interrupt Ident. Register
        signal  LCR                             : std_logic_vector(7 downto 0);  -- Line Control Register
        signal  MCR                             : std_logic_vector(7 downto 0);  -- MODEM Control Register
        signal  LSR                             : std_logic_vector(7 downto 0);  -- Line Status Register
        signal  MSR                             : std_logic_vector(7 downto 0);  -- MODEM Status Register
        signal  SCR                             : std_logic_vector(7 downto 0);  -- Scratch Register
        signal  DLL                             : std_logic_vector(7 downto 0);  -- Divisor Latch (LS)
        signal  DLM                             : std_logic_vector(7 downto 0);  -- Divisor Latch (MS)
 
        signal  DM0                             : std_logic_vector(7 downto 0);
        signal  DM1                             : std_logic_vector(7 downto 0);
 
        signal  Bit_Phase               : unsigned(3 downto 0);
        signal  RX_Filtered             : std_logic;
        signal  RX_ShiftReg             : std_logic_vector(7 downto 0);
        signal  RX_Bit_Cnt              : integer range 0 to 11;
        signal  RX_Parity               : std_logic;
        signal  RXD                             : std_logic;
 
        signal  TX_Tick                 : std_logic;
        signal  TX_ShiftReg             : std_logic_vector(7 downto 0);
        signal  TX_Bit_Cnt              : integer range 0 to 11;
        signal  TX_Parity               : std_logic;
        signal  TXD                             : std_logic;
 
begin
 
        DTR_n <= MCR(4) or not MCR(0);
        RTS_n <= MCR(4) or not MCR(1);
        OUT1_n <= MCR(4) or not MCR(2);
        OUT2_n <= MCR(4) or not MCR(3);
        SOut <= (MCR(4) or TXD) and not LCR(6);
        RXD <= SIn when MCR(4) = '0' else TXD;
 
        Intr <= not IIR(0);
 
        -- Registers
        DM0 <= DLL when LCR(7) = '1' else RBR;
        DM1 <= DLM when LCR(7) = '1' else IER;
        with A select
                D_Out <=
                        DM0 when "000",
                        DM1 when "001",
                        IIR when "010",
                        LCR when "011",
                        MCR when "100",
                        LSR when "101",
                        MSR when "110",
                        SCR when others;
        process (MR_n, XIn)
        begin
                if MR_n = '0' then
                        THR <= "00000000";
                        IER <= "00000000";
                        LCR <= "00000000";
                        MCR <= "00000000";
                        MSR <= "00000000";
                        SCR <= "00000000"; -- ??
                        DLL <= "00000000"; -- ??
                        DLM <= "00000000"; -- ??
                elsif XIn'event and XIn = '1' then
                        if Wr_n = '0' and CS_n = '0' then
                                case A is
                                when "000" =>
                                        if LCR(7) = '1' then
                                                DLL <= D_In;
                                        else
                                                THR <= D_In;
                                        end if;
                                when "001" =>
                                        if LCR(7) = '1' then
                                                DLM <= D_In;
                                        else
                                                IER(3 downto 0) <= D_In(3 downto 0);
                                        end if;
                                when "011" =>
                                        LCR <= D_In;
                                when "100" =>
                                        MCR <= D_In;
                                when "111" =>
                                        SCR <= D_In;
                                when others =>
                                end case;
                        end if;
                        if MCR(4) = '0' then
                                MSR(4) <= CTS_n;
                                MSR(5) <= DSR_n;
                                MSR(6) <= RI_n;
                                MSR(7) <= DCD_n;
                        else
                                MSR(4) <= MCR(1);
                                MSR(5) <= MCR(0);
                                MSR(6) <= MCR(2);
                                MSR(7) <= MCR(3);
                        end if;
                end if;
        end process;
 
        IIR(7 downto 3) <= "00000";
        IIR(2 downto 0) <=
                "110" when IER(2) = '1' and LSR(4 downto 1) /= "0000" else
                "110" when (IER(0) and LSR(0)) = '1' else
                "010" when (IER(1) and LSR(5)) = '1' else
                "001" when IER(3) = '1' and ((MCR(4) = '0' and MSR(3 downto 0) /= "0000") or
                                                                        (MCR(4) = '1' and MCR(3 downto 0) /= "0000")) else
                "001";
 
        -- Baud x 16 clock generator
        process (MR_n, XIn)
                variable Baud_Cnt : unsigned(15 downto 0);
        begin
                if MR_n = '0' then
                        Baud_Cnt := "0000000000000001";
                        BaudOut <= '0';
                elsif XIn'event and XIn = '1' then
                        if Baud_Cnt = "0000000000000001" or (Wr_n = '0' and CS_n = '0' and A(2 downto 1) = "00" and LCR(7) = '1') then
                                Baud_Cnt(15 downto 8) := unsigned(DLM);
                                Baud_Cnt(7 downto 0) := unsigned(DLL);
                                BaudOut <= '1';
                        else
                                Baud_Cnt := Baud_Cnt - 1;
                                BaudOut <= '0';
                        end if;
                end if;
        end process;
 
        -- Input filter
        process (MR_n, XIn)
                variable Samples : std_logic_vector(1 downto 0);
        begin
                if MR_n = '0' then
                        Samples := "11";
                        RX_Filtered <= '1';
                elsif XIn'event and XIn = '1' then
                        if RClk = '1' then
                                Samples(1) := Samples(0);
                                Samples(0) := RXD;
                        end if;
                        if Samples = "00" then
                                RX_Filtered <= '0';
                        end if;
                        if Samples = "11" then
                                RX_Filtered <= '1';
                        end if;
                end if;
        end process;
 
        -- Receive state machine
        process (MR_n, XIn)
        begin
                if MR_n = '0' then
                        RBR <= "00000000";
                        LSR(4 downto 0) <= "00000";
                        Bit_Phase <= "0000";
                        RX_ShiftReg(7 downto 0) <= "00000000";
                        RX_Bit_Cnt <= 0;
                        RX_Parity <= '0';
                elsif XIn'event and XIn = '1' then
                        if A = "000" and LCR(7) = '0' and Rd_n = '0' and CS_n = '0' then
                                LSR(0) <= '0';    -- DR
                        end if;
                        if A = "101" and Rd_n = '0' and CS_n = '0' then
                                LSR(3) <= '0';   -- FE
                                LSR(2) <= '0';   -- PE
                                LSR(1) <= '0';   -- OE
                        end if;
                        if RClk = '1' then
                                if RX_Bit_Cnt = 0 and (RX_Filtered = '1' or Bit_Phase = "0111") then
                                        Bit_Phase <= "0000";
                                else
                                        Bit_Phase <= Bit_Phase + 1;
                                end if;
                                if RX_Bit_Cnt = 0 then
                                        if Bit_Phase = "0111" then
                                                RX_Bit_Cnt <= RX_Bit_Cnt + 1;
                                                RX_Parity <= not LCR(4);        -- EPS
                                        end if;
                                elsif Bit_Phase = "1111" then
                                        RX_Bit_Cnt <= RX_Bit_Cnt + 1;
                                        if RX_Bit_Cnt = 10 then -- Parity stop bit
                                                RX_Bit_Cnt <= 0;
                                                LSR(0) <= '1'; -- UART Receive complete
                                                LSR(3) <= not RX_Filtered; -- Framing error
                                        elsif (RX_Bit_Cnt = 9 and LCR(1 downto 0) = "11") or
                                                (RX_Bit_Cnt = 8 and LCR(1 downto 0) = "10") or
                                                (RX_Bit_Cnt = 7 and LCR(1 downto 0) = "01") or
                                                (RX_Bit_Cnt = 6 and LCR(1 downto 0) = "00") then -- Stop bit/Parity
                                                RX_Bit_Cnt <= 0;
                                                if LCR(3) = '1' then    -- PEN
                                                        RX_Bit_Cnt <= 10;
                                                        if LCR(5) = '1' then    -- Stick parity
                                                                if RX_Filtered = LCR(4) then
                                                                        LSR(2) <= '1';
                                                                end if;
                                                        else
                                                                if RX_Filtered /= RX_Parity then
                                                                        LSR(2) <= '1';
                                                                end if;
                                                        end if;
                                                else
                                                        LSR(0) <= '1'; -- UART Receive complete
                                                        LSR(3) <= not RX_Filtered; -- Framing error
                                                end if;
                                                RBR <= RX_ShiftReg(7 downto 0);
                                                LSR(1) <= LSR(0);
                                                if A = "101" and Rd_n = '0' and CS_n = '0' then
                                                        LSR(1) <= '0';
                                                end if;
                                        else
                                                RX_ShiftReg(6 downto 0) <= RX_ShiftReg(7 downto 1);
                                                RX_ShiftReg(7) <= RX_Filtered;
                                                if LCR(1 downto 0) = "10" then
                                                        RX_ShiftReg(7) <= '0';
                                                        RX_ShiftReg(6) <= RX_Filtered;
                                                end if;
                                                if LCR(1 downto 0) = "01" then
                                                        RX_ShiftReg(7) <= '0';
                                                        RX_ShiftReg(6) <= '0';
                                                        RX_ShiftReg(5) <= RX_Filtered;
                                                end if;
                                                if LCR(1 downto 0) = "00" then
                                                        RX_ShiftReg(7) <= '0';
                                                        RX_ShiftReg(6) <= '0';
                                                        RX_ShiftReg(5) <= '0';
                                                        RX_ShiftReg(4) <= RX_Filtered;
                                                end if;
                                                RX_Parity <= RX_Filtered xor RX_Parity;
                                        end if;
                                end if;
                        end if;
                end if;
        end process;
 
        -- Transmit bit tick
        process (MR_n, XIn)
                variable TX_Cnt : unsigned(3 downto 0);
        begin
                if MR_n = '0' then
                        TX_Cnt := "0000";
                        TX_Tick <= '0';
                elsif XIn'event and XIn = '1' then
                        TX_Tick <= '0';
                        if RClk = '1' then
                                if TX_Cnt = "1111" then
                                        TX_Tick <= '1';
                                end if;
                                TX_Cnt := TX_Cnt + 1;
                        end if;
                end if;
        end process;
 
        -- Transmit state machine
        process (MR_n, XIn)
        begin
                if MR_n = '0' then
                        LSR(7 downto 5) <= "011";
                        TX_Bit_Cnt <= 0;
                        TX_ShiftReg <= (others => '0');
                        TXD <= '1';
                        TX_Parity <= '0';
                elsif XIn'event and XIn = '1' then
                        if TX_Tick = '1' then
                                case TX_Bit_Cnt is
                                when 0 =>
                                        if LSR(5) <= '0' then    -- THRE
                                                TX_Bit_Cnt <= 1;
                                        end if;
                                        TXD <= '1';
                                when 1 => -- Start bit
                                        TX_ShiftReg(7 downto 0) <= THR;
                                        LSR(5) <= '1';  -- THRE
                                        TXD <= '0';
                                        TX_Parity <= not LCR(4);        -- EPS
                                        TX_Bit_Cnt <= TX_Bit_Cnt + 1;
                                when 10 => -- Parity bit
                                        TXD <= TX_Parity;
                                        if LCR(5) = '1' then    -- Stick parity
                                                TXD <= not LCR(4);
                                        end if;
                                        TX_Bit_Cnt <= 0;
                                when others =>
                                        TX_Bit_Cnt <= TX_Bit_Cnt + 1;
                                        if (TX_Bit_Cnt = 9 and LCR(1 downto 0) = "11") or
                                                (TX_Bit_Cnt = 8 and LCR(1 downto 0) = "10") or
                                                (TX_Bit_Cnt = 7 and LCR(1 downto 0) = "01") or
                                                (TX_Bit_Cnt = 6 and LCR(1 downto 0) = "00") then
                                                TX_Bit_Cnt <= 0;
                                                if LCR(3) = '1' then    -- PEN
                                                        TX_Bit_Cnt <= 10;
                                                end if;
                                                LSR(6) <= '1';  -- TEMT
                                        end if;
                                        TXD <= TX_ShiftReg(0);
                                        TX_ShiftReg(6 downto 0) <= TX_ShiftReg(7 downto 1);
                                        TX_Parity <= TX_ShiftReg(0) xor TX_Parity;
                                end case;
                        end if;
                        if Wr_n = '0' and CS_n = '0' and A = "000" and LCR(7) = '0' then
                                LSR(5) <= '0';   -- THRE
                                LSR(6) <= '0';   -- TEMT
                        end if;
                end if;
        end process;
 
end;

Browse

Tools

Subversion Repositories t65

[/] [t65/] [trunk/] [rtl/] [vhdl/] [T16450.vhd] - Blame information for rev 3

Line No.	Rev	Author	Line
1	3	jesus	`--`
2			`-- 16450 compatible UART with synchronous bus interface`
3			`-- RClk/BaudOut is XIn enable instead of actual clock`
4			`-- No break detection, no modem status change detection`
5			`-- Only one stop bit supported`
6			`--`
7			`-- Version : 0208`
8			`--`
9			`-- Copyright (c) 2002 Daniel Wallner (jesus@opencores.org)`
10			`--`
11			`-- All rights reserved`
12			`--`
13			`-- Redistribution and use in source and synthezised forms, with or without`
14			`-- modification, are permitted provided that the following conditions are met:`
15			`--`
16			`-- Redistributions of source code must retain the above copyright notice,`
17			`-- this list of conditions and the following disclaimer.`
18			`--`
19			`-- Redistributions in synthesized form must reproduce the above copyright`
20			`-- notice, this list of conditions and the following disclaimer in the`
21			`-- documentation and/or other materials provided with the distribution.`
22			`--`
23			`-- Neither the name of the author nor the names of other contributors may`
24			`-- be used to endorse or promote products derived from this software without`
25			`-- specific prior written permission.`
26			`--`
27			`-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"`
28			`-- AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,`
29			`-- THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR`
30			`-- PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE`
31			`-- LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR`
32			`-- CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF`
33			`-- SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS`
34			`-- INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN`
35			`-- CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)`
36			`-- ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE`
37			`-- POSSIBILITY OF SUCH DAMAGE.`
38			`--`
39			`-- Please report bugs to the author, but before you do so, please`
40			`-- make sure that this is not a derivative work and that`
41			`-- you have the latest version of this file.`
42			`--`
43			`-- The latest version of this file can be found at:`
44			`-- http://www.opencores.org/cvsweb.shtml/t80/`
45			`--`
46			`-- Limitations :`
47			`--`
48			`-- File history :`
49			`--`
50
51			`library IEEE;`
52			`use IEEE.std_logic_1164.all;`
53			`use IEEE.numeric_std.all;`
54
55			`entity T16450 is`
56			`port(`
57			`MR_n : in std_logic;`
58			`XIn : in std_logic;`
59			`RClk : in std_logic;`
60			`CS_n : in std_logic;`
61			`Rd_n : in std_logic;`
62			`Wr_n : in std_logic;`
63			`A : in std_logic_vector(2 downto 0);`
64			`D_In : in std_logic_vector(7 downto 0);`
65			`D_Out : out std_logic_vector(7 downto 0);`
66			`SIn : in std_logic;`
67			`CTS_n : in std_logic;`
68			`DSR_n : in std_logic;`
69			`RI_n : in std_logic;`
70			`DCD_n : in std_logic;`
71			`SOut : out std_logic;`
72			`RTS_n : out std_logic;`
73			`DTR_n : out std_logic;`
74			`OUT1_n : out std_logic;`
75			`OUT2_n : out std_logic;`
76			`BaudOut : out std_logic;`
77			`Intr : out std_logic`
78			`);`
79			`end T16450;`
80
81			`architecture rtl of T16450 is`
82
83			`signal RBR : std_logic_vector(7 downto 0); -- Reciever Buffer Register`
84			`signal THR : std_logic_vector(7 downto 0); -- Transmitter Holding Register`
85			`signal IER : std_logic_vector(7 downto 0); -- Interrupt Enable Register`
86			`signal IIR : std_logic_vector(7 downto 0); -- Interrupt Ident. Register`
87			`signal LCR : std_logic_vector(7 downto 0); -- Line Control Register`
88			`signal MCR : std_logic_vector(7 downto 0); -- MODEM Control Register`
89			`signal LSR : std_logic_vector(7 downto 0); -- Line Status Register`
90			`signal MSR : std_logic_vector(7 downto 0); -- MODEM Status Register`
91			`signal SCR : std_logic_vector(7 downto 0); -- Scratch Register`
92			`signal DLL : std_logic_vector(7 downto 0); -- Divisor Latch (LS)`
93			`signal DLM : std_logic_vector(7 downto 0); -- Divisor Latch (MS)`
94
95			`signal DM0 : std_logic_vector(7 downto 0);`
96			`signal DM1 : std_logic_vector(7 downto 0);`
97
98			`signal Bit_Phase : unsigned(3 downto 0);`
99			`signal RX_Filtered : std_logic;`
100			`signal RX_ShiftReg : std_logic_vector(7 downto 0);`
101			`signal RX_Bit_Cnt : integer range 0 to 11;`
102			`signal RX_Parity : std_logic;`
103			`signal RXD : std_logic;`
104
105			`signal TX_Tick : std_logic;`
106			`signal TX_ShiftReg : std_logic_vector(7 downto 0);`
107			`signal TX_Bit_Cnt : integer range 0 to 11;`
108			`signal TX_Parity : std_logic;`
109			`signal TXD : std_logic;`
110
111			`begin`
112
113			`DTR_n <= MCR(4) or not MCR(0);`
114			`RTS_n <= MCR(4) or not MCR(1);`
115			`OUT1_n <= MCR(4) or not MCR(2);`
116			`OUT2_n <= MCR(4) or not MCR(3);`
117			`SOut <= (MCR(4) or TXD) and not LCR(6);`
118			`RXD <= SIn when MCR(4) = '0' else TXD;`
119
120			`Intr <= not IIR(0);`
121
122			`-- Registers`
123			`DM0 <= DLL when LCR(7) = '1' else RBR;`
124			`DM1 <= DLM when LCR(7) = '1' else IER;`
125			`with A select`
126			`D_Out <=`
127			`DM0 when "000",`
128			`DM1 when "001",`
129			`IIR when "010",`
130			`LCR when "011",`
131			`MCR when "100",`
132			`LSR when "101",`
133			`MSR when "110",`
134			`SCR when others;`
135			`process (MR_n, XIn)`
136			`begin`
137			`if MR_n = '0' then`
138			`THR <= "00000000";`
139			`IER <= "00000000";`
140			`LCR <= "00000000";`
141			`MCR <= "00000000";`
142			`MSR <= "00000000";`
143			`SCR <= "00000000"; -- ??`
144			`DLL <= "00000000"; -- ??`
145			`DLM <= "00000000"; -- ??`
146			`elsif XIn'event and XIn = '1' then`
147			`if Wr_n = '0' and CS_n = '0' then`
148			`case A is`
149			`when "000" =>`
150			`if LCR(7) = '1' then`
151			`DLL <= D_In;`
152			`else`
153			`THR <= D_In;`
154			`end if;`
155			`when "001" =>`
156			`if LCR(7) = '1' then`
157			`DLM <= D_In;`
158			`else`
159			`IER(3 downto 0) <= D_In(3 downto 0);`
160			`end if;`
161			`when "011" =>`
162			`LCR <= D_In;`
163			`when "100" =>`
164			`MCR <= D_In;`
165			`when "111" =>`
166			`SCR <= D_In;`
167			`when others =>`
168			`end case;`
169			`end if;`
170			`if MCR(4) = '0' then`
171			`MSR(4) <= CTS_n;`
172			`MSR(5) <= DSR_n;`
173			`MSR(6) <= RI_n;`
174			`MSR(7) <= DCD_n;`
175			`else`
176			`MSR(4) <= MCR(1);`
177			`MSR(5) <= MCR(0);`
178			`MSR(6) <= MCR(2);`
179			`MSR(7) <= MCR(3);`
180			`end if;`
181			`end if;`
182			`end process;`
183
184			`IIR(7 downto 3) <= "00000";`
185			`IIR(2 downto 0) <=`
186			`"110" when IER(2) = '1' and LSR(4 downto 1) /= "0000" else`
187			`"110" when (IER(0) and LSR(0)) = '1' else`
188			`"010" when (IER(1) and LSR(5)) = '1' else`
189			`"001" when IER(3) = '1' and ((MCR(4) = '0' and MSR(3 downto 0) /= "0000") or`
190			`(MCR(4) = '1' and MCR(3 downto 0) /= "0000")) else`
191			`"001";`
192
193			`-- Baud x 16 clock generator`
194			`process (MR_n, XIn)`
195			`variable Baud_Cnt : unsigned(15 downto 0);`
196			`begin`
197			`if MR_n = '0' then`
198			`Baud_Cnt := "0000000000000001";`
199			`BaudOut <= '0';`
200			`elsif XIn'event and XIn = '1' then`
201			`if Baud_Cnt = "0000000000000001" or (Wr_n = '0' and CS_n = '0' and A(2 downto 1) = "00" and LCR(7) = '1') then`
202			`Baud_Cnt(15 downto 8) := unsigned(DLM);`
203			`Baud_Cnt(7 downto 0) := unsigned(DLL);`
204			`BaudOut <= '1';`
205			`else`
206			`Baud_Cnt := Baud_Cnt - 1;`
207			`BaudOut <= '0';`
208			`end if;`
209			`end if;`
210			`end process;`
211
212			`-- Input filter`
213			`process (MR_n, XIn)`
214			`variable Samples : std_logic_vector(1 downto 0);`
215			`begin`
216			`if MR_n = '0' then`
217			`Samples := "11";`
218			`RX_Filtered <= '1';`
219			`elsif XIn'event and XIn = '1' then`
220			`if RClk = '1' then`
221			`Samples(1) := Samples(0);`
222			`Samples(0) := RXD;`
223			`end if;`
224			`if Samples = "00" then`
225			`RX_Filtered <= '0';`
226			`end if;`
227			`if Samples = "11" then`
228			`RX_Filtered <= '1';`
229			`end if;`
230			`end if;`
231			`end process;`
232
233			`-- Receive state machine`
234			`process (MR_n, XIn)`
235			`begin`
236			`if MR_n = '0' then`
237			`RBR <= "00000000";`
238			`LSR(4 downto 0) <= "00000";`
239			`Bit_Phase <= "0000";`
240			`RX_ShiftReg(7 downto 0) <= "00000000";`
241			`RX_Bit_Cnt <= 0;`
242			`RX_Parity <= '0';`
243			`elsif XIn'event and XIn = '1' then`
244			`if A = "000" and LCR(7) = '0' and Rd_n = '0' and CS_n = '0' then`
245			`LSR(0) <= '0'; -- DR`
246			`end if;`
247			`if A = "101" and Rd_n = '0' and CS_n = '0' then`
248			`LSR(3) <= '0'; -- FE`
249			`LSR(2) <= '0'; -- PE`
250			`LSR(1) <= '0'; -- OE`
251			`end if;`
252			`if RClk = '1' then`
253			`if RX_Bit_Cnt = 0 and (RX_Filtered = '1' or Bit_Phase = "0111") then`
254			`Bit_Phase <= "0000";`
255			`else`
256			`Bit_Phase <= Bit_Phase + 1;`
257			`end if;`
258			`if RX_Bit_Cnt = 0 then`
259			`if Bit_Phase = "0111" then`
260			`RX_Bit_Cnt <= RX_Bit_Cnt + 1;`
261			`RX_Parity <= not LCR(4); -- EPS`
262			`end if;`
263			`elsif Bit_Phase = "1111" then`
264			`RX_Bit_Cnt <= RX_Bit_Cnt + 1;`
265			`if RX_Bit_Cnt = 10 then -- Parity stop bit`
266			`RX_Bit_Cnt <= 0;`
267			`LSR(0) <= '1'; -- UART Receive complete`
268			`LSR(3) <= not RX_Filtered; -- Framing error`
269			`elsif (RX_Bit_Cnt = 9 and LCR(1 downto 0) = "11") or`
270			`(RX_Bit_Cnt = 8 and LCR(1 downto 0) = "10") or`
271			`(RX_Bit_Cnt = 7 and LCR(1 downto 0) = "01") or`
272			`(RX_Bit_Cnt = 6 and LCR(1 downto 0) = "00") then -- Stop bit/Parity`
273			`RX_Bit_Cnt <= 0;`
274			`if LCR(3) = '1' then -- PEN`
275			`RX_Bit_Cnt <= 10;`
276			`if LCR(5) = '1' then -- Stick parity`
277			`if RX_Filtered = LCR(4) then`
278			`LSR(2) <= '1';`
279			`end if;`
280			`else`
281			`if RX_Filtered /= RX_Parity then`
282			`LSR(2) <= '1';`
283			`end if;`
284			`end if;`
285			`else`
286			`LSR(0) <= '1'; -- UART Receive complete`
287			`LSR(3) <= not RX_Filtered; -- Framing error`
288			`end if;`
289			`RBR <= RX_ShiftReg(7 downto 0);`
290			`LSR(1) <= LSR(0);`
291			`if A = "101" and Rd_n = '0' and CS_n = '0' then`
292			`LSR(1) <= '0';`
293			`end if;`
294			`else`
295			`RX_ShiftReg(6 downto 0) <= RX_ShiftReg(7 downto 1);`
296			`RX_ShiftReg(7) <= RX_Filtered;`
297			`if LCR(1 downto 0) = "10" then`
298			`RX_ShiftReg(7) <= '0';`
299			`RX_ShiftReg(6) <= RX_Filtered;`
300			`end if;`
301			`if LCR(1 downto 0) = "01" then`
302			`RX_ShiftReg(7) <= '0';`
303			`RX_ShiftReg(6) <= '0';`
304			`RX_ShiftReg(5) <= RX_Filtered;`
305			`end if;`
306			`if LCR(1 downto 0) = "00" then`
307			`RX_ShiftReg(7) <= '0';`
308			`RX_ShiftReg(6) <= '0';`
309			`RX_ShiftReg(5) <= '0';`
310			`RX_ShiftReg(4) <= RX_Filtered;`
311			`end if;`
312			`RX_Parity <= RX_Filtered xor RX_Parity;`
313			`end if;`
314			`end if;`
315			`end if;`
316			`end if;`
317			`end process;`
318
319			`-- Transmit bit tick`
320			`process (MR_n, XIn)`
321			`variable TX_Cnt : unsigned(3 downto 0);`
322			`begin`
323			`if MR_n = '0' then`
324			`TX_Cnt := "0000";`
325			`TX_Tick <= '0';`
326			`elsif XIn'event and XIn = '1' then`
327			`TX_Tick <= '0';`
328			`if RClk = '1' then`
329			`if TX_Cnt = "1111" then`
330			`TX_Tick <= '1';`
331			`end if;`
332			`TX_Cnt := TX_Cnt + 1;`
333			`end if;`
334			`end if;`
335			`end process;`
336
337			`-- Transmit state machine`
338			`process (MR_n, XIn)`
339			`begin`
340			`if MR_n = '0' then`
341			`LSR(7 downto 5) <= "011";`
342			`TX_Bit_Cnt <= 0;`
343			`TX_ShiftReg <= (others => '0');`
344			`TXD <= '1';`
345			`TX_Parity <= '0';`
346			`elsif XIn'event and XIn = '1' then`
347			`if TX_Tick = '1' then`
348			`case TX_Bit_Cnt is`
349			`when 0 =>`
350			`if LSR(5) <= '0' then -- THRE`
351			`TX_Bit_Cnt <= 1;`
352			`end if;`
353			`TXD <= '1';`
354			`when 1 => -- Start bit`
355			`TX_ShiftReg(7 downto 0) <= THR;`
356			`LSR(5) <= '1'; -- THRE`
357			`TXD <= '0';`
358			`TX_Parity <= not LCR(4); -- EPS`
359			`TX_Bit_Cnt <= TX_Bit_Cnt + 1;`
360			`when 10 => -- Parity bit`
361			`TXD <= TX_Parity;`
362			`if LCR(5) = '1' then -- Stick parity`
363			`TXD <= not LCR(4);`
364			`end if;`
365			`TX_Bit_Cnt <= 0;`
366			`when others =>`
367			`TX_Bit_Cnt <= TX_Bit_Cnt + 1;`
368			`if (TX_Bit_Cnt = 9 and LCR(1 downto 0) = "11") or`
369			`(TX_Bit_Cnt = 8 and LCR(1 downto 0) = "10") or`
370			`(TX_Bit_Cnt = 7 and LCR(1 downto 0) = "01") or`
371			`(TX_Bit_Cnt = 6 and LCR(1 downto 0) = "00") then`
372			`TX_Bit_Cnt <= 0;`
373			`if LCR(3) = '1' then -- PEN`
374			`TX_Bit_Cnt <= 10;`
375			`end if;`
376			`LSR(6) <= '1'; -- TEMT`
377			`end if;`
378			`TXD <= TX_ShiftReg(0);`
379			`TX_ShiftReg(6 downto 0) <= TX_ShiftReg(7 downto 1);`
380			`TX_Parity <= TX_ShiftReg(0) xor TX_Parity;`
381			`end case;`
382			`end if;`
383			`if Wr_n = '0' and CS_n = '0' and A = "000" and LCR(7) = '0' then`
384			`LSR(5) <= '0'; -- THRE`
385			`LSR(6) <= '0'; -- TEMT`
386			`end if;`
387			`end if;`
388			`end process;`
389
390			`end;`