G成 繁锁霜男在 44密的团变(B△<b) 表3-20 四位数值比较器真值表 比较输入 级联输入 输出 01043B3 A,B, A, B 1 lo Bo(ab)(asb)(a=b)(4>B)(A<B)44=B) 1(, >B ① ××××× ×× A2B 0d101073 3 ××××× × 3=B3A2B2×××××× 01010042=B A,<B,×××× 0②14=B342=B2A>B1×××× A,=B A=B A<B 0101A2=B A2B2A1=B1A0>B0×× A=B 01010 A2=B2,41=B A<B B B2AB Ao=Ba 0101010100 00 ③ A=B =B A=B 4=B B3A2=B2 A=B, A0-Bo表3-20 四位数值比较器真值表 ① ② ③ 比 较 输 入 级 联 输 入 输 出 A3 B3 A2 B2 A1 B1 A0 B0 (a>b) (a<b) (a=b) (A>B) (A<B) (A=B) A3>B3 A3<B3 A3 =B3 A3 =B3 A3 =B3 A3 =B3 A3 =B3 A3 =B3 A3 =B3 A3 =B3 A3 =B3 × × × × A2>B2 A2<B2 A2 =B2 A2 =B2 A2 =B2 A2 =B2 A2 =B2 A2 =B2 A2 =B2 × × × × × × × × A1>B1 A1<B1 A1 =B1 A1 =B1 A1 =B1 A1 =B1 A1 =B1 × × × × × × × × × × × × A0>B0 A0<B0 A0 =B0 A0 =B0 A0 =B0 × × × × × × × × × × × × × × × × × × × × × × × × 1 0 0 0 1 0 0 0 1 1 0 0 0 1 0 1 0 0 0 1 0 1 0 0 0 1 0 1 0 0 0 1 0 1 0 0 0 1 0 0 0 1 注：①只要两数最高位不等，就可以判断 两数大小。其余各位可以为任意值。 ②③若高位相等，则需要比较低位。 若A、B两数各位均相等，输出状态取 决于级联输入状态。 Ai =Bi Ai  Bi =1 =1 Ai Bi Ai>Bi Ai<Bi Ai Bi =1 ( ) ( ) 3 3 2 2 1 1 0 0 3 3 2 2 1 1 0 0 3 3 3 3 2 2 3 3 2 2 1 1 A B A B A B A B a b A B A B A B A B A B A B A B A B A B A B A B +          +        = +   +     ( ) ( ) 3 3 2 2 1 1 0 0 3 3 2 2 1 1 0 0 3 3 3 3 2 2 3 3 2 2 1 1 A B A B A B A B a b A B A B A B A B A B A B A B A B A B A B A B +          +        = +   +     ( ) ( ) A = B = A3 B3 • A2 B2 • A1 B1 • A0 B0 • a = b