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--key_scan.vhd keypress scaner 
library ieee ; 
use ieee.std_logic_1164.all; 
use ieee.std_logic_unsigned.all; 
use work.components.all; 
entity key_scan is 
port( 
  col : in std_logic_vector(3 downto 0);--keybord column state 
  scan_cnt : in std_logic_vector(3 downto 0);--keybord scan location 
  row : out std_logic_vector(3 downto 0);--keybord row state 
  key_pressed : out std_logic);--key_pressed->0 unkey_pressed->1 
end key_scan; 
architecture behavior of key_scan is 
begin  
  row<="1110" when scan_cnt(3 downto 2)="00" else--row scan 
       "1101" when scan_cnt(3 downto 2)="01" else 
       "1011" when scan_cnt(3 downto 2)="10" else 
       "0111"; 
  key_pressed<=col(0) when scan_cnt(1 downto 0)="00" else--colum scan 
               col(1) when scan_cnt(1 downto 0)="01" else 
               col(2) when scan_cnt(1 downto 0)="10" else 
               col(3); 
end behavior;