第三 組合邏輯電根據組合邏輯電路的不同特點，數字電路分成：組合邏輯電路（組合電路時序邏輯電路（時序電路

fiA1，A2An

組合邏輯電路的分析方法：1）

LAB分析加法 半加器真值不考慮由低位進位來的加法 SAA11SABCIABCIABCIABCICOACIABBCI

S“1時，S1”CI“1時，CICIAA

(2)1A3A2A1A0B3B3B3B3 A0

每位進位信號作為高位的輸入信號――故任一位的加法運算必須在低一位的運算完成后才能進行――2、超前進 0

ENSiAiBi

CiAiBiAiBi74LS1534個輸入數據中選出所要得輸出總結：122n選一的數據選擇器可nn個輸入變量的邏輯函數

D0A1A0 DX DX

D1A1A0

D2A1A0

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

Y(A>B)

AA

組合邏輯電路設計的一般步驟：1) ABC00

8線－38線－3 IY3

Y2I4I5I6I7I4I5I6IY1I2I3I6I7I2I3I6IY0I1I3I5I7I1I3I5I 二－十進制優先編碼器（ IIIIIIIYYY Y0I9I7I8I9I5I6I8I9I3I4I6I8I9I1I2I4I6I8IY1I7I8I9I6I8I9I3I4I5I8I9I2I4I5I8IY2I7I8I9I6I8I9I5I8I9I4I8IY3I8I1 YYYYY0A2A1A0，Y1A2A1A0

111E6 Y2A2A1A0，Y3A2A1A0，Y4A2A1A0，Y5A2A1A0，Y6A2A1A0，Y7A2A1A0由邏輯表達式畫出邏輯圖（54頁Y0A3A2A1A0，Y1A3A2A1A0，Y2A3A2A1A0，Y3A3A2A1A0Y4A3A2A1A0，Y5A3A2A1A0，Y6A3A2A1A0，Y7A3A2A1A0Y8A3A2A1A0，Y9A3A2A1A0由邏輯表達式畫出邏輯圖（55頁YYYYYY3842100102a,d,e,g段點亮。以前所述的組合邏輯電路，設tpd0，實際上tpd0。由于由輸入到輸出，不同的路L

A BBLLAC

A=B=1時，L應為“1”C無關，但當C10時，輸出出現負跳變冒1FABACB=C=0FAAFACABBC2LACBCA=B=1LCCLACBC3A B

MSI74LS153（41）FABABAB

EN

74LS151（81）FABCABCABCABFABCABCABCABCYD0ABCD1ABCD2ABCD3ABCD4ABCD5ABCD6ABCD774LS153（41）FABCABCABC解：FFAB)CAB)CAB)C則有：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