二位數值比較器是由四個輸入端和三個輸出端組成的比較器，實現兩個二位二進位制數大小的比較（用高低電平來表示輸入輸出）真值表如下：

（xx表任意狀態）
因此設計時，定義4個輸入端和3個輸出端的實體，分別為A1A0,B1B0和f1(a>b)f2(a<b)f3(a=b)
具體程式碼如下：

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
ENTITY homework2 IS
	PORT(A1:IN STD_LOGIC;             --定義4個輸入端和3個輸出端
		 A0:IN STD_LOGIC;
		 B1:IN STD_LOGIC;
		 B0:IN STD_LOGIC;
		 f1:OUT STD_LOGIC;
		 f2:OUT STD_LOGIC;
		 f3:OUT STD_LOGIC);
END homework2;
ARCHITECTURE HA OF homework2 IS
SIGNAL tmp:STD_LOGIC_VECTOR(3 DOWNTO 0);--定義一個訊號陣列
BEGIN
tmp<=A1 & B1 & A0 & B0;                 --用&連線四個輸入值，並賦值給tmp
PROCESS(tmp)
BEGIN
	CASE tmp IS                         --CASE語句實現具體程式碼
		WHEN "0000" =>f1<='0';f2<='0';f3<='1';
		WHEN "0001" =>f1<='0';f2<='1';f3<='0';
		WHEN "0010" =>f1<='1';f2<='0';f3<='0';
		WHEN "0011" =>f1<='0';f2<='0';f3<='1';
		WHEN "0100" =>f1<='0';f2<='1';f3<='0';
		WHEN "0101" =>f1<='0';f2<='1';f3<='0';
		WHEN "0110" =>f1<='0';f2<='1';f3<='0';
		WHEN "0111" =>f1<='0';f2<='1';f3<='0';
		WHEN "1000" =>f1<='1';f2<='0';f3<='0';
		WHEN "1001" =>f1<='1';f2<='0';f3<='0';
		WHEN "1010" =>f1<='1';f2<='0';f3<='0';
		WHEN "1011" =>f1<='1';f2<='0';f3<='0';
		WHEN "1100" =>f1<='0';f2<='0';f3<='1';
		WHEN "1101" =>f1<='0';f2<='1';f3<='0';
		WHEN "1110" =>f1<='1';f2<='0';f3<='0';
		WHEN "1111" =>f1<='0';f2<='0';f3<='1';
	END CASE;
END PROCESS;
END HA;
 

模擬結果如下：