问题 问答题

某计算机系统的CPU有20条地址线(A19~A0),8条数据线(D7~DO)和一条控制线

,主存按字节编址,由16KB的ROM和64KB的RAM组成。拟采用8K×4的ROM芯片2片(编号①、②),8K×8的ROM芯片1片(编号③号),32K×2的RAM芯片4片(编号④~⑦号),32K×8的RAM芯片1片(编号⑧号)。要求:
①、②号芯片的地址范围为:18000H~19FFFH
③号芯片的地址范围为:F8000H~F9FFFH
④~⑦号芯片的地址范围为:98000H~9FFFFH
⑧号芯片的地址范围为:B8000H~BFFFFH
给出芯片/芯片组的片选逻辑,并画出cPu与各存储芯片的连接图。

答案

参考答案:据题中各存储芯片/芯片组的地址范围,可分析出片选逻辑表达式分别为:
①、②号芯片:[*]
③号芯片:[*]
④~⑦号芯片:[*]
⑧号芯片:[*]
地址译码方案:用地址线A19A18A17作为译码器的输入,A16A15经过“与门”连接译码器的使能控制端G端,由于G端必须为高电平译码器才能正常工作,所以A16A15始终都为高电平,与门的输出才为高电平,保证译码器正常工作。假设各存储器芯片的片选信号为低电平有效,所以可用译码器的输出和地址线A14A13经过或门选中①、②号芯片,[*]及A14A13经过或门选中③芯片,选中④~⑦号芯片,选中⑧号芯片。
存储器与CPU的连接如下图所示。
[*]

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