Re: assignment #3 part 1

Ed Casas (edc@ece.ubc.ca) Sun, 27 Feb 2000 08:03:23 -0800 

Date: Sun, 27 Feb 2000 08:03:23 -0800
From: Ed Casas <edc@ece.ubc.ca>
Subject: Re: assignment #3 part 1



On Sat, Feb 26, 2000 at 05:39:10PM -0800, a student asked:

> Hi there, I'm somewhat confused about the ROM for this assgnment.  Is it
> supposed to output the instruction (i.e. PUSH, POP, DUP, etc. ) or is it
> supposed to output something else?

The instruction.

> I think that the address that it takes in is the PC at that
> particular clock cycle.  Where is the memory that we are using
> for the look up?

The ROM is the memory.  It "looks up" and outputs the instruction
for a given address.

> I have this so far for the architecture for the rom.
> 
> architecture rtl of rom is
> begin
>     data <=  -- the instruction given at "address", address of what memory?
> 
> end rtl;

A ROM can be described in VHDL as a selected assignment.  See
Lecture 1.  Page 3 describes the operation of a ROM and page 4
describes the use of a selected assignment to implement arbitrary
logic functions (the example is an LED decoder).

> As you can see I'm lost.

> I'm into my 5th hour of just trying to figure out what is being ask of me
> for the rom, I am quite frustrated at this point.

Quite a few people seem to be mystified by how computer programs
are represented in memory.  I had assumed the encoding and
storage of computer programs in memory was covered in ELEC 259.

We can talk about this on Monday.

> ... I just have never taken this long to figure out what a
> question is asking of me.

Feel free to ask sooner.

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