Re: Is microprocessor an integrated circuit???

From: keith (krw_at_att.bizzzz)
Date: 01/29/05 

Date: Fri, 28 Jan 2005 22:42:22 -0500

On Fri, 28 Jan 2005 13:56:46 -0500, Spehro Pefhany wrote:

> On Fri, 28 Jan 2005 01:21:29 GMT, the renowned mzenier@eskimo.com
> (Mark Zenier) wrote:
>
>>In article <uZTJd.187$Eh5.115@trnddc04>, Bradley1234 <someone@yahoo.com> wrote:
>>>PLEASE show an example of a microprocessor that doesnt use microcode
>>
>>Most of them have their control unit logic implemented in a PLA
>>(Programmable Logic Array) which directly implements a two level logic
>>equation. With microcode, there would be an address that was decoded
>>to provide a word (or row) of the ROM's contents. There's no such thing
>>as an address in a PLA, just inputs and outputs.
>
> If you have a PLA and a ROM in a black box, and are allowed to observe
> the outputs only after they have settled, what difference is there
> between the two?

Sure, sorta. I can tell a ROM from a PLA, but perhaps not a PLA from a
ROM. Think about a 2D map of inputs vs outputs. A PLA (after arranging
the I/O) will have square holes in the map 2^n in size. A ROM likely
won't. Given a random change of inputs, a ROM will also have a
probabilitiy of a change of outputs greater than that of a PLA. Or put
another way, a PLA contians less information than a ROM. 

-- 
  Keith
Quantcast