Path: utzoo!attcan!uunet!cs.utexas.edu!usc!apple!apple.com!teener
From: teener@apple.com (Michael Teener)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Double termination on a //ci ??
Message-ID: <7128@goofy.Apple.COM>
Date: 10 Mar 90 07:35:36 GMT
Sender: usenet@Apple.COM
Organization: Apple Computer
Lines: 29
References:<-531597662@cpl-mfh.UUCP> <49073@coherent.coherent.com>

In article <49073@coherent.coherent.com> dplatt@coherent.com (Dave Platt) 
writes:
> If you have a IIci and an external hard disk, you'd be best off to have
> two terminators:  one attached to the external hard drive (either on the
> drive controller or plugged into the drive case's SCSI port), and one at
> the IIci end of the bus.  Unfortunately, the Mac does not use the
> standard 50-pin SCSI jack... it uses a DB-25... and it's not easy to
> find SCSI terminators that use DB-25 connectors.

This is generally correct, but it is important to note that if your IIci 
has an *internal* hard disk, it is already terminated once (we include a 
termination in all our internal drives).  Do not put *three* terminators 
(internal and two external) on the SCSI bus, this will overload the 5380 
line drivers.  

Also, if the IIci doesn't have an internal hard disk and only has *one* 
external SCSI device, then a single termination at that device will work 
... providing that the SCSI system cable (25-to-34 pin) is nice and short 
(like the one we sell ... now you know why the sucker is so inconveniently 
short).  If you have more than one external SCSI device and no internal 
drive, then put terminators at the first and last device in the chain.  
Since we are now guaranteed to have adequate termination, we can make the 
SCSI peripheral cable (34-to-34 pin) fairly long.

---- Michael Teener -- 408-974-3521 ---------------------------------+
---- Internet teener@apple.com, AppleLink TEENER                     |
---- Apple may know my opinions, but *I* am responsible for them     |
---------------------------------------------------------------------+
Transportation by Cheetah N9900U, a loyal beast for the past 6 years.