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Path: utzoo!utgpu!lharris
From: lharris@gpu.utcs.toronto.edu (Leonard Harris)
Date: Wed, 24-Feb-88 19:19:34 EST
Message-ID: <1988Feb24.191934.16031@gpu.utcs.toronto.edu>
Organization: University of Toronto Computing Services
Newsgroups: comp.sys.atari.st
Subject: Re: Re: tried to 1 meg, problem
References: <118chad@byuvax.bitnet>
Reply-To: lharris@gpu.utcs.UUCP (Leonard Harris)

The reason for putting 68 ohm resistors on the CAS lines is due to the
lack of an efficient ground plane on the ST.  The resistors are there to reduce
ringing on these lines which causes the memory to be "double-clocked" - ie. 
think valid data is there when it isn't.  A better idea would have been to 
actively terminate these lines, but a series resistor is cheaper and seems
to work.  (note: this is a reason many 4 meg add on boards don't work when
fully loaded on the ST - they are too noisy and CAS gets confused)
/leonard