URL
https://opencores.org/ocsvn/z80soc/z80soc/trunk
Subversion Repositories z80soc
[/] [z80soc/] [trunk/] [V0.7/] [DE1/] [vhdl/] [keyboard.VHD] - Rev 40
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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;
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