吉林大学：《数字逻辑电路》课程电子教案（PPT课件）第六章 采用中、大规模集成电路的逻辑设计

& (A>B) (A=B) B & (A<B) 一位比较器 函数表达式(A>B)=AAB=A(A+B)=AB (A<B)=BAB=B(A+B)=AB (A=B)=(A>B)+(A<B) =AB+AB=A①B

函数表达式 (A  B) = AAB = A(A + B) = AB 一位比较器 (A=B) A B & (A>B) (A<B) & & 1 (A  B) = BAB = B(A + B) = AB AB AB A B A B A B A B = + =  ( = ) = (  ) + (  )

7485型四位数字比较器功能表 比较输入 级联输入 输出 A3,B3 A2,B2A1,B1 A0,B0 (A<B) (A=B)I(A>B) (A<B)o (A=B)o (A>B)o A3>B3 中 中 血 中 中 中 0 0 1 A3<B3 必 φ φ d 0 1 0 0 A3=B3 A2>B2 φ 血 φ 0 0 1 A3=B3 A2<B2 中 0 φ 0 0 A3=B3A2=B2A1>B1 0 φ φ 0 0 1 A3=B3A2=B2A1<B1 φ 血 中 血 1 0 0 A3=B3 A2=B2 A=BI A0>B0 φ φ 0 0 0 A3=B3 A2=B2 A=B Ao<Bo φ φ 0 1 0 0 A3=B3 A2=B2 A1=BI A0=B0 0 0 1 0 0 A3=B3 A2-B2 AI=BI A0=B0 1 0 0 0 0 A3=B3 A2=B2 A=BI A0=B0 0 0 0 1 0 A3-B3A2-B2A1=B1 A0=B0 1 0 0 1 0 A3=B3 A2=B2 A1=B1 A0=B0 1 0 1 0 0 0 A3=B3A2=B2A1=B1 A0-B0 0 0 0 1 0 1

7485 型四位数字比较器功能表 比较输入 级联输入 输出 A3,B3 A2,B2 A1,B1 A0,B0 (A<B)I (A=B)I (A>B)I (A<B)O (A=B)O (A>B)O A3>B3       0 0 1 A3<B3       1 0 0 A3=B3 A2>B2      0 0 1 A3=B3 A2<B2      1 0 0 A3=B3 A2=B2 A1>B1     0 0 1 A3=B3 A2=B2 A1<B1     1 0 0 A3=B3 A2=B2 A1=B1 A0>B0    0 0 1 A3=B3 A2=B2 A1=B1 A0<B0    1 0 0 A3=B3 A2=B2 A1=B1 A0=B0 0 0 1 0 0 1 A3=B3 A2=B2 A1=B1 A0=B0 1 0 0 1 0 0 A3=B3 A2=B2 A1=B1 A0=B0 0 1 0 0 1 0 A3=B3 A2=B2 A1=B1 A0=B0  1  0 1 0 A3=B3 A2=B2 A1=B1 A0=B0 1 0 1 0 0 0 A3=B3 A2=B2 A1=B1 A0=B0 0 0 0 1 0 1

(4>B)=4B i=0,1,23 (4<B)=AB, i=0,1,2,3 (A=B=A,(4,B)+B(4,B)=A田B

Ai = Bi Ai Ai Bi + Bi Ai Bi = Ai  Bi ( )＝ ( ) ( ) ( ) 0,1,2,3 ( ) 0,1,2,3  = =  = = A B A B i A B A B i i i i i i i i i

(A>B)o=(A3=B(A=B2 )(A=B)(A=Bo)(A=B) +(A3=B3(A2=B2(A=B(A=B(A<B)1 +(4<B3)+(A3=B)(A<B2) +(A,=B(A,=B2(A<B) +(4=B(A4=B2(4=B(Ao<Bo) (A<B)0=(4,=BXA,=B2(4=BX4,=BA=B) +(4,=B(A,=B2A=B(A=B(A>B)1 +(A3>B)+(A=B3(A2>B2) +(A=B(A,=B2(A>B) +(A=B3(A2=B2(A=B)(A>B) (A=B)0=(4=B3(42=B2XA=B(A=B(A=B)

( )( )( )( ) ( )( )( ) ( ) ( )( ) ( )( )( )( )( ) ( ) ( )( )( )( )( ) 3 3 2 2 1 1 0 0 3 3 2 2 1 1 3 3 3 3 2 2 3 3 2 2 1 1 0 0 3 3 2 2 1 1 0 0 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 A B A B A B A B I O I + = = =  + = =  +  + =  + = = = =   = = = = = = ( )( )( )( ) ( )( )( ) ( ) ( )( ) ( )( )( )( )( ) ( ) ( )( )( )( )( ) 3 3 2 2 1 1 0 0 3 3 2 2 1 1 3 3 3 3 2 2 3 3 2 2 1 1 0 0 3 3 2 2 1 1 0 0 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 A B A B A B A B I O I + = = =  + = =  +  + =  + = = = =   = = = = = = A B O A B A B A B A B A B I ( ) ( )( )( )( )( ) = = 3 = 3 2 = 2 1 = 1 0 = 0 =

(A<B) Bo B1 B2 B3 Ao A1 A2 A3 (A>B) (A=B)0 (A<B) 74LS85逻辑图

B0 B1 B2 B3 A0 A1 A2 A3 (A<B)I (A>B)I (A=B)I (A<B)o (A=B)o (A>B)o 74LS85逻辑图