《IO译码习题答案》PPT课件.ppt

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1、第二章I/O端口地址译码技术习题答案Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.1.已知并行接口芯片8255A有4个端口，片选信号CS为低电平有效。试设计一个译码电路，使该芯片的4个端口地址为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译码器AY0BY1CY2G1Y3Y4G2AY5Y6G2BY700010&A3A4A5+5VA6A7A8A9AENIORIOWPC总线&端口译码电路2.读图计算译码地址Ev

3、aluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.3.设计一个译码电路，要求产生2A8H～2AFH共8个端口地址的选通信号Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.解：由于要产生8个端口的地址信号，因此适合选用3-8译码器74LS138。

4、对应的地址关系为Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.4.设计端口地址为218H的译码电路Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.分析CPU执行IN/OUT指令时，发出端口的地址信号MOVDX,218HINAL,DX或O

5、UTDX,AL对应218H端口的地址信号为（取A9~A0）：A9A8A7A6A5A4A3A2A1A0(地址信号)1000011000B218H只要满足此地址取值的译码电路均可Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.译码电路部分满足：只当地址信号A9~A0为：A9A8A7A6A5A4A3A2A1A01000011000即218H时，输出0，使I/O接口的CS有效否则输出1使I/O接口

6、的CS无效PC总线数据线DBRDWRCS端口译码电路0A9A8A7A6A5A4A3A2A1A0AENIORIOWI/O接口D0~D7D0~D710000110000&方法一、用门电路实现Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.PC总线数据线DBRDWRCS端口译码电路0A9A8A7A6A5A4A3A2A1A0AENIORIOWI/O接口D0~D7D0~D710000110000&注

7、意译码电路中：由于高位地址线A15~A10未参与译码,即:地址A15~A0为：××××××1000011000均能输出0,所以该电路使：一个端口对应多个地址共26=64个218，618,A18，E18等等方法一、用门电路实现Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.PC总线74LS30为8输入与非门74LS20为4输入与非门74LS32为2输入或门当地址信号为：A9A8A7A6A5A

8、4A3A2A1A01000011000即地址为218H或门74LS32输出0，使I/O接口的CS有效。I/O接口RDWRCSD0~D7数据线DB端口译码电路0A9A8A7A6A5