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1、時序邏輯電路(290)功能表R0(1)、R0(2)——置“0”端S9(1)、S9(2)——置“9”端，CPA單獨接入脈沖，F(xiàn)A構(gòu)成二進制計數(shù)器。CPB單獨接入脈沖，F(xiàn)BFCFD構(gòu)成五進制計數(shù)器。外部時鐘CP是先送到CPA還是先送到CPB，在QDQCQBQA這四個輸出端會形成不同的碼制。2CPACPBR0(1)R0(2)S9(2)S9(1)NCNCVCCQAQDQBQCGND1234567141312111098QAQDQBQCS9(2)S9(1)R0(2)R0(1)CP1CPA74LS9074LS90管腳分布圖3常用符號QAQBQCQDCPA74LS90CPB
2、S9(1)S9(0)R0(1)R0(1)4(1)CPA單獨接入脈沖，F(xiàn)A構(gòu)成二進制計數(shù)器。二進制計數(shù)器SdC1Rd&&CPAQAS9(1)S0(2)R0(2)R0(1)1J1KF0SdC1Rd1JC1RdRdSdC1Rd1J&&CP0CPBQ0QBQCQDS9(1)S9(2)R0(2)R0(1)C11K1J1K1J1K1KFAFBFCFD5(2)CP1單獨接入脈沖，F(xiàn)BFCFD構(gòu)成五進制計數(shù)器。1JC1RdRdSdC1Rd1J&CPBQBQCQDR0(2)R0(1)C11K1J1K1KFBFCFD&S9(1)S0(2)SdC1Rd&CP0Q0S0(1)S9(2
3、)1J1KFA五進制計數(shù)器6分析1JC1RdRdSdC1Rd1J&CPBQBQCQDR0(2)R0(1)C11K1J1K1KFBFCFD&S9(1)S9(2)7功能表0001111011001111010101111011101111110010111010008(3)CPA接入脈沖，QA接CPB脈沖，F(xiàn)AFBFCFD構(gòu)成8421碼計數(shù)器。SdC1Rd1JC1RdRdSdC1Rd1J&&CPACPBQAQBQCQDS9(1)S9(2)R0(2)R0(1)C11K1J1K1J1K1KFAFBFCFDCPB=QAQA變化，提供CPB脈沖。9(4)CPB接入脈沖，Q
4、D接CPA脈沖，F(xiàn)AFBFCFD構(gòu)成5421碼計數(shù)器。SdC1Rd1JC1RdRdSdC1Rd1J&&CPACPBQAQBQCQDS9(1)S9(2)R0(2)R0(1)C11K1J1K1J1K1KFAFBFCFDCPA=QDQD變化，提供CPA脈沖。10用7490構(gòu)成任意進制計數(shù)器例1：用7490構(gòu)成七進制計數(shù)器QDQCQBQA000000010010001101000101011001111000100111QAQBQCQDCPA74LS90CPBS9(1)S9(0)R0(1)R0(1)&實現(xiàn)電路QDQCQBQA0000000100100011010001
5、010110011110001001請看EDA：90計數(shù)器(七進制）.ca412例2：用7490構(gòu)成八進制計數(shù)器QDQCQBQA000000010010001101000101011001111000100113QAQBQCQDCPA74LS90CPBS9(1)S9(0)R0(1)R0(1)實現(xiàn)電路QDQCQBQA0000000100100011010001010110011110001001請看EDA：90計數(shù)器(八進制）.ca414例2：用7490構(gòu)成53進制計數(shù)器QDQCQBQA00000001001000110100010101100111100010
6、01QDQCQBQA0000000100100011010001010110011110001001高位低位15QAQBQCQDCPA74LS90CPBS9(1)S9(0)R0(1)R0(1)實現(xiàn)電路QAQBQCQDCPA74LS90CPBS9(1)S9(0)R0(1)R0(1)高位低位&16結(jié)束17此課件下載可自行編輯修改，僅供參考！ 感謝您的支持，我們努力做得更好！謝謝
