*BSD News Article 6752


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From: st923150@pip.cc.brandeis.edu (Benjamin A. Tober)
Subject: Re: Question on Diamond Clock Synthesizer
Message-ID: <1992Oct19.223502.20477@news.cs.brandeis.edu>
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Reply-To: st923150@pip.cc.brandeis.edu
Organization: Brandeis University
References: <1992Oct19.082420.16353@Informatik.TU-Muenchen.DE> <1992Oct19.151409.24581@osf.org> <1992Oct19.190736.11988@fcom.cc.utah.edu>,<1992Oct19.215256.5037@osf.org>
Date: Mon, 19 Oct 1992 22:35:02 GMT
Lines: 29

I agree with the esteemed Mr. Crudup.  It might be possible to overheat
component(s) on the video board by using a very small divisor, if the board
were so poorly designed as to have components that cannot tolerate a 
frequency that _can_ be generated.  Historical note:  The Tandy CoCo
had a problem like this:  The processor and bus local to the processor
were driven by a programmable oscillator which could run the processor
at speeds faster than its design parameters.  It is, thus, one of the few
machines on which there is a known way to nicely smoke the motherboard
using a two-line program written with the built-in BASIC interpreter, but
I digress...  So, as to whether it is possible to damage the board by
misprogramming it, the answer is yes if it was so designed.  Now, on the other
hand, as for destroying the monitor, if it is a multifrequency monitor
(i.e.- the kind usually used with such a board) then it is extremely
unlikely that malprogramming the clock generator could cause damage.  
Multifreqency monitors _attempt_ to match the output frequency of the
board driving them, but only within a certain range.  In general, they
are designed to just "give up" on frequencies outside of the intended
range.  This would usually be witnessed as rolling or other general
unintelligibility of the display...  Now, as for damaging a 
fixed-frequency monitor, this is very much possible.  IBM fixed-frequency
monochrome monitors (which were meant to be used with the MDA) could
be caused to overheat by certain screen-blankers which blanked the screen
by turning off the sync signals to the monitor.  So, certainly, when dealing
with fixed-frequency monitors, care must be exercized.
In summary, whether it is possible to damage the board by misprogramming
the clock generator, only some EE(s) at Diamond would know... or, if you
want to hardware reverse-engineer the beast, be my guest.  As for damaging
multifrequency monitors, I would place money on this not being possible.
-ben