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1、第二章I/O端口地址譯碼技術(shù)習(xí)題答案Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.1.已知并行接口芯片8255A有4個(gè)端口，片選信號(hào)CS為低電平有效。試設(shè)計(jì)一個(gè)譯碼電路，使該芯片的4個(gè)端口地址為2F0H～2F3H。Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011
2、AsposePtyLtd.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.200~207h208~20Fh210~217h218~21Fh220~227h228~22Fh230~237h238~24Fh74LS1383-8譯碼器AY0BY1CY2G1Y3Y4G2AY5Y6G2BY700010&A3A4A5+5VA6A7A8A9AENIORIOWPC總線&端口譯碼電路2.讀圖計(jì)算譯碼地址Ev
3、aluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.3.設(shè)計(jì)一個(gè)譯碼電路，要求產(chǎn)生2A8H～2AFH共8個(gè)端口地址的選通信號(hào)Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.解：由于要產(chǎn)生8個(gè)端口的地址信號(hào)，因此適合選用3-8譯碼器74LS138。
4、對(duì)應(yīng)的地址關(guān)系為Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.4.設(shè)計(jì)端口地址為218H的譯碼電路Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.分析CPU執(zhí)行IN/OUT指令時(shí)，發(fā)出端口的地址信號(hào)MOVDX,218HINAL,DX或O
5、UTDX,AL對(duì)應(yīng)218H端口的地址信號(hào)為（取A9~A0）：A9A8A7A6A5A4A3A2A1A0(地址信號(hào))1000011000B218H只要滿足此地址取值的譯碼電路均可Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.譯碼電路部分滿足：只當(dāng)?shù)刂沸盘?hào)A9~A0為：A9A8A7A6A5A4A3A2A1A01000011000即218H時(shí)，輸出0，使I/O接口的CS有效否則輸出1使I/O接口
6、的CS無效PC總線數(shù)據(jù)線DBRDWRCS端口譯碼電路0A9A8A7A6A5A4A3A2A1A0AENIORIOWI/O接口D0~D7D0~D710000110000&方法一、用門電路實(shí)現(xiàn)Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.PC總線數(shù)據(jù)線DBRDWRCS端口譯碼電路0A9A8A7A6A5A4A3A2A1A0AENIORIOWI/O接口D0~D7D0~D710000110000&注
7、意譯碼電路中：由于高位地址線A15~A10未參與譯碼,即:地址A15~A0為：××××××1000011000均能輸出0,所以該電路使：一個(gè)端口對(duì)應(yīng)多個(gè)地址共26=64個(gè)218，618,A18，E18等等方法一、用門電路實(shí)現(xiàn)Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.PC總線74LS30為8輸入與非門74LS20為4輸入與非門74LS32為2輸入或門當(dāng)?shù)刂沸盘?hào)為：A9A8A7A6A5A
8、4A3A2A1A01000011000即地址為218H或門74LS32輸出0，使I/O接口的CS有效。I/O接口RDWRCSD0~D7數(shù)據(jù)線DB端口譯碼電路0A9A8A7A6A5
