Помогите с ПЛИС, начинающему разобраться.

[vlad]

Вот для примера сделал реализацию простого интерфейса опроса клавиатуры:

Схема:
Вложение 33296

library IEEE;
use IEEE.STD_LOGIC_1164.all;

entity keyb is
  port(
    CLK    : in std_logic;
    C      : in std_logic_vector(3 downto 0);
    R      : out std_logic_vector(3 downto 0);
    SCAN0  : out std_logic_vector(7 downto 0);
    SCAN1  : out std_logic_vector(7 downto 0);
    KEY    : out std_logic
  );
end keyb;

architecture keyb of keyb is
  type state_t is (s_idle, s0, s1, s2, s3);
  signal state  : state_t := s_idle;
  signal row    : std_logic_vector(3 downto 0) := "0000";
  signal data0  : std_logic_vector(3 downto 0) := "1111";
  signal data1  : std_logic_vector(3 downto 0) := "1111";
  signal data2  : std_logic_vector(3 downto 0) := "1111";
  signal data3  : std_logic_vector(3 downto 0) := "1111";
  signal K      : std_logic;
  
begin
  process  (CLK)
  begin
    if CLK'event and CLK = '1' then
      if state = s_idle then
        row <= "0000";
        data0 <= "1111";
        data1 <= "1111";
        data2 <= "1111";
        data3 <= "1111";
        if K /= '1' then
          row <= "1110";
          state <= s0;
        end if;
      elsif state = s0 then
        if K /= '1' then
          data0 <= C;
        end if;
        row <= "1101";
        state <= s1;
      elsif state = s1 then
        if K /= '1' then
          data1 <= C;
        end if;
        row <= "1011";
        state <= s2;
      elsif state = s2 then
        if K /= '1' then
          data2 <= C;
        end if;
        row <= "0111";
        state <= s3;
      elsif state = s3 then
        if K /= '1' then
          data3 <= C;
        end if;
        row <= "0000";
        state <= s_idle;
      end if;
    end if;
  end process;
  K     <= C(3) and C(2) and C(1) and C(0);
  R     <= row;
  SCAN0 <= data0 & data1;
  SCAN1 <= data2 & data3;
  KEY   <= K;
end keyb;

Моделирование:
Вложение 33297