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;