Subversion Repositories z80soc

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-- This design is part of:

-- Z80SoC (Z80 System on Chip)

-- Ronivon Candido Costa

-- ronivon.costa@gmail.com

--

-- 2010 - 11 - 22

--

LIBRARY IEEE;

USE  IEEE.STD_LOGIC_1164.all;

USE  IEEE.STD_LOGIC_ARITH.all;

USE  IEEE.STD_LOGIC_UNSIGNED.all;

ENTITY keyboard IS

        PORT(   keyboard_clk, keyboard_data, clock ,

                        reset, read             : IN    STD_LOGIC;

                        scan_code               : OUT   STD_LOGIC_VECTOR(7 DOWNTO 0);

                        scan_ready              : OUT   STD_LOGIC);

END keyboard;

ARCHITECTURE a OF keyboard IS

        SIGNAL INCNT                                    : std_logic_vector(3 downto 0);

        SIGNAL SHIFTIN                                  : std_logic_vector(8 downto 0);

        SIGNAL READ_CHAR, clock_enable  : std_logic;

        SIGNAL INFLAG, ready_set                : std_logic;

        SIGNAL keyboard_clk_filtered    : std_logic;

        SIGNAL filter                                   : std_logic_vector(7 downto 0);

BEGIN

PROCESS (read, ready_set)

BEGIN

  IF read = '1' THEN scan_ready <= '0';

  ELSIF ready_set'EVENT and ready_set = '1' THEN

                scan_ready <= '1';

  END IF;

END PROCESS;

--This process filters the raw clock signal coming from the keyboard using a shift register and two AND gates

Clock_filter: PROCESS

BEGIN

        WAIT UNTIL clock'EVENT AND clock= '1';

        clock_enable <= NOT clock_enable;

        IF clock_enable = '1' THEN

                filter (6 DOWNTO 0) <= filter(7 DOWNTO 1) ;

                filter(7) <= keyboard_clk;

                IF filter = "11111111" THEN keyboard_clk_filtered <= '1';

                ELSIF  filter= "00000000" THEN keyboard_clk_filtered <= '0';

                END IF;

        END IF;

END PROCESS Clock_filter;

--This process reads in serial data coming from the terminal

PROCESS

BEGIN

WAIT UNTIL (KEYBOARD_CLK_filtered'EVENT AND KEYBOARD_CLK_filtered='1');

IF RESET='0' THEN

        INCNT <= "0000";

        READ_CHAR <= '0';

        ready_set<= '0';

ELSE

  IF KEYBOARD_DATA='0' AND READ_CHAR='0' THEN

        READ_CHAR<= '1';

                ready_set<= '0';

  ELSE

                        -- Shift in next 8 data bits to assemble a scan code

    IF READ_CHAR = '1' THEN

        IF INCNT < "1001" THEN

                INCNT                           <= INCNT + 1;

                SHIFTIN(7 DOWNTO 0) <= SHIFTIN(8 DOWNTO 1);

                SHIFTIN(8)                      <= KEYBOARD_DATA;

                        -- End of scan code character, so set flags and exit loop

        ELSE

                        scan_code                       <= SHIFTIN(7 DOWNTO 0);

                        READ_CHAR                       <= '0';

                ready_set                       <= '1';

                INCNT                           <= "0000";

        END IF;

     END IF;

   END IF;

 END IF;

END PROCESS;

END a;