Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!cica!gatech!bbn!bbn.com!levin
From: levin@bbn.com (Joel B Levin)
Newsgroups: comp.sys.mac
Subject: Re: Hopping on the SCSI bus (uptown)
Message-ID: <43584@bbn.COM>
Date: 1 Aug 89 13:52:37 GMT
References: <8907312149.AA18252@ucbvax.Berkeley.EDU> <3262@internal.Apple.COM>
Sender: news@bbn.COM
Reply-To: levin@BBN.COM (Joel B Levin)
Organization: BBN Communications Corporation
Lines: 30

In article <3262@internal.Apple.COM> teener@apple.com (Michael Teener) writes:
|Here is some useful information for SCSI configuration problems:
 . . .
|What all this means is: (1) put a device you will always want powered on 
|at the far end of the SCSI chain *and attach a terminator* and (2) if you 
|do not have an internal drive do the same for the first peripheral device 
|(terminator + always powered on).
 . . .
|(Note: if you have non-Apple peripherals then there is no guarantee that 
|terminators follow our philosophy ... read the manual and note any 
|comments about termination and power-on requirements.)

I have just been through some of this, and can concur.  I have an SE
with internal HD and have just attached an external foreign drive.
The new drive comes with terminators, and there is a jumper to select
whether the terminators receive power from the drive or from the SCSI
cable.  Currently they are powered from the drive; when that is turned
off the SCSI bus is dead and the Mac will only boot from and recognize
floppies.  Unfortunately, I am told, neither the SE nor the Plus puts
terminator power out on the cable (possibly because there are fewer
pins at the Mac end), so changing the jumper would be worse; then the
terminators would never get power.  So I have to live with
disconnecting the drive from the bus if I wish to run with it powered
down.

	/JBL
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