Xref: utzoo tor.general:315 ont.general:411
Path: utzoo!yunexus!spectrix!clewis
From: clewis@spectrix.UUCP (Chris R. Lewis)
Newsgroups: tor.general,ont.general
Subject: Re: Pointer to XT clone motherboards needed
Message-ID: <416@spectrix.UUCP>
Date: 29 Jan 88 16:25:52 GMT
Article-I.D.: spectrix.416
Posted: Fri Jan 29 11:25:52 1988
References: <84@sickkids.UUCP>
Reply-To: clewis@spectrix.UUCP (Chris R. Lewis)
Distribution: ont
Organization: Spectrix Microsystems Inc., Toronto, Ontario, Canada
Lines: 33

In article <84@sickkids.UUCP> mark@sickkids.UUCP (Mark Bartelt) writes:
>Quick IBM PC question ...
>I have managed to locate one dealer who sells a different type of turbo board.
>It will allegedly switch between the two in response to some magic keystroke,
>but the people who sell this don't know exactly what the code that does this
>actually *does* to select one clock or the other.
>...Presumably all I need to do in
>order to change clocks is "outb someport,somevalue".  But they can't tell me
>what the "someport" and "somevalue"(s) are.  Sigh.

You should be very careful with purchasing any XT boards if you wish
to be able to change clock speed by program control.  Most of the boards 
I'm familiar with (STM products) do this with a parallel bit on the 
keyboard controller.

The keyboard controller is usually a single chip CPU that contains
mask ROM, lots of parallel I/O etc.  An Intel 8047 I think.  The ROM
does all of the keyboard decoding, debounce and generates the keyboard
scan codes.  When it sees the hot key sequence, it merely flips a bit
that changes the main CPU clock.  In laptops it also quite frequently has
an analog output to adjust brightness.

Unfortunately, the main CPU CANNOT get at the I/O ports on the keyboard 
controller.  The ol' "you can't get there from here" problem)  Thus, 
the only way to change speed is via the keyboard, but not by program.

In contrast, an Intel 386 can do it by program control.

The technical manuals for the board should make this clear.
-- 
Chris Lewis, Spectrix Microsystems Inc,
UUCP: {uunet!mnetor, utcsri!utzoo, lsuc, yunexus}!spectrix!clewis
Phone: (416)-474-1955