双2－4译码器：74139.txt

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-- Dual 2-to-4 Decoder
-- A set of conditional signal assignments model a dual 2-to-4 decoder
-- uses 1993 std VHDL
-- download from: www.pld.com.cn & www.fpga.com.cn

library IEEE;
use IEEE.Std_logic_1164.all;


entity HCT139 is  
   port(A2, B2, G2BAR, A1, B1, G1BAR : in std_logic;
            Y20, Y21, Y22, Y23, Y10, Y11, Y12, Y13 : out std_logic);
end HCT139;

architecture VER1 of HCT139 is
begin
   Y10 <= '0' when (B1 = '0') and ((A1 = '0') and (G1BAR = '0')) else '1';  
   Y11 <= '0' when (B1 = '0') and ((A1 = '1') and (G1BAR = '0')) else '1';
   Y12 <= '0' when (B1 = '1') and ((A1 = '0') and (G1BAR = '0')) else '1';
   Y13 <= '0' when (B1 = '1') and ((A1 = '1') and (G1BAR = '0')) else '1';
   Y20 <= '0' when (B2 = '0') and ((A2 = '0') and (G2BAR = '0')) else '1';  
   Y21 <= '0' when (B2 = '0') and ((A2 = '1') and (G2BAR = '0')) else '1';
   Y22 <= '0' when (B2 = '1') and ((A2 = '0') and (G2BAR = '0')) else '1';
   Y23 <= '0' when (B2 = '1') and ((A2 = '1') and (G2BAR = '0')) else '1';
end VER1