Re: newbie question: Memory maped IO vs Port IO

From: Michael R. Kesti (mkesti_at_gv.net)
Date: 03/13/04 

Date: Fri, 12 Mar 2004 21:10:47 -0800

gt wrote:

>Could someone explain memory mapped IO and Port IO?

Some processors provide seperate address space for I/O. When they do,
they have a control bus signals, in addition to read and write signals,
that select whether the address bus currently holds a memory or a port
address. These signals are driven according to the machine instructions
being executed at the time.

>When should I use one or the other?

When a processor provides no seperate port addressing you have no choice.
Otherwise, whether you use one or the other is a function of the hardware
design.

> why some devices
>support port IO only?

Processors come in a great many flavors, each with their own variations.
Whether they provide seperate memory and port spaces is just one of those
variations and is one of the many things to be considered when choosing
a processor for an application. 

-- 
========================================================================
          Michael Kesti            |  "And like, one and one don't make
                                   |   two, one and one make one."
          mkesti@gv.net            |          - The Who, Bargain

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