From: paws@spam.cray.com (Daniel Baehr)
Subject: Re: GVP/SyQuest SOLVED!
Organization: Cray Research, Inc.
Date: 20 Aug 92 07:05:53 CDT


In article <20AUG199207201130@ariel.lerc.nasa.gov>, smneyln@ariel.lerc.nasa.gov (Michael Neylon) writes:
> By pulling out the terminating resistors at the back of the SyQuest, I
> got both my GVP s.II (a500+), and the 44m SQ to work.  But this lead me
> to thinking on how the GVP SCSI chain is set up.  I offer the following
> proposal, in no way is this meant to be taken as the absolute truth
> (in other words IMHO).
> 
> My SCSI looks like this:
> 
> 55Meg Quantum (in GVP) -----> SuQuest ---> SCSI #2 ----> #3 ---->
>     SCSI #0                   SCSI #1
> 
> 	#4------> #5-----> #6-----> GVPscsi.device ---> to computer
> 					SCSI #7
> 

   What is the " to computer " part?  Are you looping back into the
 computer or what??

> Now, according to the GVP manual, the quantum has no terminating resistors
> on it (this was verified).  Without the SyQuest in the chain, the SCSI
> controller would see the scsi.dev, followed by the Quantum.  No problem
> (SCSI scans backwards along the chain (from 7 to 0) by my understanding)
> 
> However, I had first installed the SyQuest WITH the term. resistors on it.
> Now, the controller saw the GVPscsi.dev, followed by the SyQuest.  It DOES
> NOT see the Quantum.  Thus, when the Quantum tries to validate itself, 
> the controller doesnt recongnized the device, and barfs at it.  (This
> explains the 'Unexpected Status' warning).
> 
> So, by removing the resistors, the Quantum is now visible to the scsi.dev,
> and everything proceeds hunky dorry...
> 
> MORAL:  GVP LIES!  According to the manual, it says that additional devices
> should follow the rule of thumb: the last one should have a term. resistor.
> However, if this is done, all the devices before the last on the chain will
> not be validated, and you lose those drives.

   Nope.  In this case they are correct.  The last physical device on 
 EITHER END of the SCSI bus should have the termination.  I was looking  
 at my HCII/+8 and the way the drive is connected up and the way the 
 external port goes off board is wrong as far as the SCSI termination
 goes.  The short cable that connects the internal drive is not
 terminated on the drive end.  To use an external device properly with
 ,at least in my case, the HCII/+8 I should remove the termination on 
 the card, terminate the internal drive and terminate the LAST PHYSICAL
 device that is external to the controller.  You SHOULD do it this way
 but you dont HAVE to UNTIL you start to push the speed of the SCSI
 bus.  Then I bet you'll start to get R/W errors from the internal drive
 because of reflection off the unterminated end.

> 
> Please correct me if I am incorrect...I still plan on getting a CD-ROM
> drive once they become super cheap, but I do not want this problem to 
> reoccur.  I am just hoping that the removal of the Term. resistors on
> the SyQuest was not a fluke, but it has worked thru 10+ resets/powerups...
> 
> Michael Neylon   aka Masem the Great and Almighty Thermodynamics GOD!
>       //         | Senior, Chemical Engineering, Univ. of Toledo
>   \\ // Only the |   Summer Intern, NASA Lewis Research Center
> \  \X/   AMIGA!  |          smneyln@ariel.lerc.nasa.gov              /
>  --------+ How do YOU spell 'potato'?  How 'bout 'lousy'? +----------
>     "Me and Spike are big Malcolm 10 supporters." - J.S.,P.L.C.L
--
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| Daniel Baehr Work: paws@spam.cray.com  Home: daniel_baehr@bearsden.UUCP|
| These OPINIONS are mine and mine alone.                                |
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