电子技术讲义 第三章 组合逻辑电路

第三 组合逻辑电根据组合逻辑电路的不同特点，数字电路分成：组合逻辑电路（组合电路时序逻辑电路（时序电路

fiA1，A2An

组合逻辑电路的分析方法：1）

LAB分析加法 半加器真值不考虑由低位进位来的加法 SAA11SABCIABCIABCIABCICOACIABBCI

S“1时，S1”CI“1时，CICIAA

(2)1A3A2A1A0B3B3B3B3 A0

每位进位信号作为高位的输入信号――故任一位的加法运算必须在低一位的运算完成后才能进行――2、超前进 0

ENSiAiBi

CiAiBiAiBi74LS1534个输入数据中选出所要得输出总结：122n选一的数据选择器可nn个输入变量的逻辑函数

D0A1A0 DX DX

D1A1A0

D2A1A0

D3A1A01AB比较YABAB，YABABABA⊙B，YABY2(AY3(A

Y(A>B)

AA

组合逻辑电路设计的一般步骤：1) ABC00

8线－38线－3 IY3

Y2I4I5I6I7I4I5I6IY1I2I3I6I7I2I3I6IY0I1I3I5I7I1I3I5I 二－十进制优先编码器（ IIIIIIIYYY Y0I9I7I8I9I5I6I8I9I3I4I6I8I9I1I2I4I6I8IY1I7I8I9I6I8I9I3I4I5I8I9I2I4I5I8IY2I7I8I9I6I8I9I5I8I9I4I8IY3I8I1 YYYYY0A2A1A0，Y1A2A1A0

111E6 Y2A2A1A0，Y3A2A1A0，Y4A2A1A0，Y5A2A1A0，Y6A2A1A0，Y7A2A1A0由逻辑表达式画出逻辑图（54页Y0A3A2A1A0，Y1A3A2A1A0，Y2A3A2A1A0，Y3A3A2A1A0Y4A3A2A1A0，Y5A3A2A1A0，Y6A3A2A1A0，Y7A3A2A1A0Y8A3A2A1A0，Y9A3A2A1A0由逻辑表达式画出逻辑图（55页YYYYYY3842100102a,d,e,g段点亮。以前所述的组合逻辑电路，设tpd0，实际上tpd0。由于由输入到输出，不同的路L

A BBLLAC

A=B=1时，L应为“1”C无关，但当C10时，输出出现负跳变冒1FABACB=C=0FAAFACABBC2LACBCA=B=1LCCLACBC3A B

MSI74LS153（41）FABABAB

EN

74LS151（81）FABCABCABCABFABCABCABCABCYD0ABCD1ABCD2ABCD3ABCD4ABCD5ABCD6ABCD774LS153（41）FABCABCABC解：FFAB)CAB)CAB)C则有：A1=A，A0=BD10C，D11=1，D12=01Y0A3A2A1A0m0，Y1A3A2A1A0m1，Y2A3A2A1A0m214A3E6Y3A3A2A1A0m3，Y4A3A2A1A0m4，Y5A3A2A1A0m5，Y6A3A2A1A0m6，Y7A3A2A1A0m7，Y8A3A2A1A0m8，Y9A3A2A214A3E674LS138FABCABCFABCABCABC

m1m3 74LS138Y1A,B,CABCABCABCABC，Y2A,B,CABCABCABCY1ABCABCABCABCABCm1m2m4m7m1m2m4Y2A,B,CABCABCABCABCm3m5m6m7m3m5m62214

1414 2 2Y0A2A1A0S1S2S3Y1A2A1A0S1S2S3Y2A2AA0SSS，Y3A2AASS