Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watnot!watmath!clyde!cbatt!ihnp4!ptsfa!lll-lcc!seismo!columbia!rutgers!cbmvax!daveh
From: daveh@cbmvax.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: CLtd 20M hard disk
Message-ID: <1479@cbmvax.cbmvax.cbm.UUCP>
Date: Mon, 2-Mar-87 13:22:09 EST
Article-I.D.: cbmvax.1479
Posted: Mon Mar  2 13:22:09 1987
Date-Received: Wed, 4-Mar-87 19:01:43 EST
References: <256@mcdsun.UUCP>
Organization: Commodore Technology, West Chester, PA
Lines: 51

in article <256@mcdsun.UUCP>, fnf@mcdsun.UUCP (Fred Fish) says:
> Keywords: Cltd 20M hard disk troubles
> 
> Both venders have been helpful in attempting to cure the problem.  So
> far, I attribute it a poorly designed hardware expansion architecture
> with respect to bus noise and reflections.
> 
> ASDG has promised to send me a version of their Minirack which buffers
> the bus at the connector, rather than adding several inches to it internally
> as my current Minirack-C does.  My ultimate solution will probably be to
> sell off all my current hardware and buy a 2000 as soon as they become
> available, unless I decide to jump ship and buy one of the new high end
> Macs due (as rumor has it) to be announced on Monday.
> 
> -Fred

Just a point of information: anyone who's not buffering the 86 pin edge
connector is not conforming to the expansion specification.  From Chapter
physical.new, page 8, of the Amiga "Schematics and Expansion Specifications"

	4. Loading

		There is 1 AMP available on the plus 5 volts.

		Put your buffers as close to [86 pin] connector as you
		possibly can.

		You can put one 74F load on each signal.

Any board that follows these rules shouldn't have any loading problem.
There are a few signals that sometimes can't be buffered, but the main
one (address, data, strobes, etc.) must be.  Also, there's a good amount
of timing constraints that must also be followed; some Amiga specific,
some based on the timing specification of an 8MHz 68000.  I'll bet you that
most of the boards that are having trouble are violating some of these
design rules.  I don't personally have access to any of these expansion 
devices, so I'm not stating that they categorically violate any of the
given rules.  But these rules were written up for a specific reason -- to
be followed!  If a manufacturer breaks them, all the fast PALs in the world
may not help.
-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                   __  ____    ____    _____   _____   _____
Dave Haynie                       /// / _  |  / __ \  /  _  \ /  _  \ /  _  \
Commodore Technology             /// / / | | /_/  | | | | | | | | | | | | | |
                            |\  /// / /__| |  ____/ | | | | | | | | | | | | |
                            |\\/// / ____  | / ____/  | | | | | | | | | | | |
                             \\// / /    | | | |____  | |_| | | |_| | | |_| |
{ihnp4,etc.}!cbmvax!daveh     \/ /_/     |_| \______| \_____/ \_____/ \_____/

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~