Re: Assignment 4 - Q1&2

Ed Casas (edc@ece.ubc.ca) Wed, 29 Nov 2000 09:35:18 -0800 

Date: Wed, 29 Nov 2000 09:35:18 -0800
From: Ed Casas <edc@ece.ubc.ca>
Subject: Re: Assignment 4 - Q1&2



> I don't see how the memory devices we are given in Q1 can
> completely fill the address space spanned by the given 20-bit
> CPU address bus.

They don't.  This is usually the case.  For example, the CPU your
PC may have a 32-bit address bus (4 GB) but few people have this
much memory installed.

> If so, how can I completely decode the CPU addresses for Q2 ?

Design a circuit that enables each bank only for its range of
addresses.  

Since chip memory sizes are always powers of two, address
decoders simply recognize a particular combination of certain
high-order address bits.

> Do we need to add extra RAM and ROM banks for Q2 ?

No, use only enough banks to make up the the amount of memory
required by Q1.

-- 
Ed Casas   edc@ece.ubc.ca   http://casas.ece.ubc.ca   +1 604 822-2592