Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!batcomputer!rpi!pawl9.pawl.rpi.edu!ncc1701
From: ncc1701@pawl.rpi.edu (Mark O. Chadwick)
Newsgroups: comp.sys.tandy
Subject: Re: Silence?
Message-ID: <1092@rpi.edu>
Date: 3 Apr 89 20:06:57 GMT
References: <14051@gryphon.COM>
Sender: usenet@rpi.edu
Organization: Rensselaer Polytechnic Institute, Troy, NY
Lines: 41

In article <14051@gryphon.COM> gmadison@pnet02.cts.com (George Madison) writes:
>I recently posted some rumours about the Model 4 and the Zilog Z280 CPU,
>centering around the (admittedly slim) possibility that Tandy might, in an
>effort to cut production costs, redesign the 4D to use the much more powerful
>chip.
>
>I know there are Model 4 users on here, as well as people who work at Tandy
>itself.  I rather expected some comment from users, as well as (perhaps)
>statements from those at Tandy that they can't say anything one way or the
>other.
>
>I was *not* expecting utter silence on the issue!  There must be at least a
>*little* interest out there.....?

Okay, okay...I thought you were getting deluges of mail, so I didn't bother
saying anything.  

I thought about doing such a conversion, but the idea fell flat on its face
when I took a good look at the system's configuration.

First of all, changing the clock to support the Z280's higher clock speed 
would not be a good idea, since the RS232, video timing, and several other
timing signals are generated from it.  My problem is that they are generated
in a custom chip, and can't be changed without building a new one from 
scratch.  So, you'd be stuck with either a clock running at 4 or 5 MHz, or
building a separate clock and have the system slightly out of skew...

Secondly, the model IV does not have anywhere near the ideal overall power
that I would like to make such a change worthwhile, so I have decided to
build a system from scratch, using 4 Z280's in parallel along with assorted
Z80's, 680x0's, coprocessors, etc...

My point is, that unless you're willing to go through a huge hardware and
software update, it's either better to get a new computer or design one
from scratch.  The model IV's architecture is just too closed for any 
major modifications like that.

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 (Mark Chadwick)           |    captain...and my friend