gistfile1.txt

-- Floppy disk read data pulse catcher
-- Eric Smith <[email protected]>
-- 2016-08-02
-- WARNING: untested

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

entity floppy_rd_pulse_catcher is
  port (clk:                 in  std_logic;
        async_read_data_n:   in  std_logic;  -- active low
        sync_read_data:      out std_logic   -- active high
        );
end floppy_rd_pulse_catcher;

architecture behavioral of floppy_rd_pulse_catcher is
  signal q1, q2: std_logic;
begin
  process (async_read_data_n, clk)
  begin
    if async_read_data_n = '0' then
      q1 <= '1';
    elsif rising_edge (clk) then
      q1 <= '0';
    end if;
    
    if rising_edge(clk) then
      q2 <= q1;
    end if;
  end process;

  sync_read_data <= '1' when q1 = '1' and q2 = '0'
               else '0';
end behavioral;