Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!columbia!rutgers!caip!cbmvax!daveh
From: daveh@cbmvax.cbm.UUCP (Dave Haynie)
Newsgroups: net.micro.apple
Subject: Re: Re: C128 vs Apple //e
Message-ID: <822@cbmvax.cbmvax.cbm.UUCP>
Date: Wed, 1-Oct-86 17:21:22 EDT
Article-I.D.: cbmvax.822
Posted: Wed Oct  1 17:21:22 1986
Date-Received: Fri, 3-Oct-86 11:50:00 EDT
References: <284@neoucom.UUCP>
Organization: Commodore Technology, West Chester, PA
Lines: 39

> Summary: cpu clock speed faster in c128
> 
> [Line eater, get me.]
> 
> It's been a while since I was dabbling on a c128.  I do remember,
> though, that under certain circumstances the cpu on the  c128 is
> run at 2.04 MHz, rather than the "standard" 1.02 MHz.  Don't quote me
> on this, but I think it was durring the CRT retrace times that the
> cpu is running faster on the c128.

Its been awhile since I dabbled on the C128 too.  But I was one of the
design engineers on the thing.  The 1.02 Mhz speed, same as the C64, is
what you get if you want to use both displays on the '128 (40 and 80
column, which are distinct video controllers).  The 40 column display
chip, when active, will alos steal a few cycles from the processor for
character data fetches and sprite display.  However, if the 40 column 
display is not needed, the '128 will run at 2.04 MHz nearly all the
time, and the 80 column display chip will function as normal.  The 
2.04 MHz clock will slow down for two things.  RAM refresh is one of 
these, though its pretty infrequent.  The other slowdown is for any
access of an I/O chip.  You'll get a slowdown statistically 50% of the
time you access an I/O chip.  The reason behind this is that some of
the I/O chips require the 1.02 MHz clock as a time base.  Thus, if the
I/O request occurs out of sync with the 1.02 MHz clock, it must be
stretched to sync.  If the access is in sync, no stretch is required.
And there are no video DMA's to slow the processor down in this mode;
the 80 column chip manages its own memory.
> 
> Bill Mayhew
> Division of Basic Medical Sciences
> Northeastern Ohio Universities' College of Medicine
> Rootstown, Ohio  44272  USA    216-325-2511
> (wtm@neoucom.UUCP)
-- 
============================================================================
Dave Haynie    {caip,ihnp4,allegra,seismo}!cbmvax!daveh

	These opinions are my own, though if you try them out, and decide
	that you really like them, a small donation would be appreciated.