Re: Assignment3

Ed Casas (edc@ece.ubc.ca) Sun, 27 Feb 2000 17:23:43 -0800 

Date: Sun, 27 Feb 2000 17:23:43 -0800
From: Ed Casas <edc@ece.ubc.ca>
Subject: Re: Assignment3



On Sun, Feb 27, 2000 at 04:48:19PM -0800, Jonathan Lashin wrote:
> What does it mean when it says that:
> 
> 'the CPU retrives and instruction from the ROM
> location addressed by PC and executes it in one clock
> cycle' ?

The assignment says "...retrieves an instruction..."

> Does this mean that the whole thing happens in one clock cycle,
> or that the retrieval is one cycle and the execution is one
> more clock cycle?

It means that both things (retrieval and execution) happen in one
clock cycle.

> Wouldn't it need one clock cycle to get the instruction and one
> to execute it?

No.

A read from a ROM (or RAM for that matter) only involves
combinational logic.  The delay through the ROM can be treated in
the same way as the delay through any other piece of
combinational logic that lies between register outputs and
register inputs.

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