Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!bionet!apple!apple.com!teener
From: teener@apple.com (Michael Teener)
Newsgroups: comp.sys.mac
Subject: Re: Hopping on the SCSI bus (uptown)
Message-ID: <3262@internal.Apple.COM>
Date: 1 Aug 89 02:06:50 GMT
References: <8907312149.AA18252@ucbvax.Berkeley.EDU>
Sender: usenet@Apple.COM
Organization: Apple Computer
Lines: 37

Here is some useful information for SCSI configuration problems:

1) the Mac+ does not have any internal termination for SCSI.

2) the MacSE and MacII only have termination for SCSI *if* there is an 
internal hard disk.

3) you are required to have at least one termination for SCSI.

4) you are required to have two terminations for SCSI (one on each end of 
the bus) if there is more than one SCSI peripheral device (we get to cheat 
... a Mac without an internal drive does not count as a SCSI device).

5) all of our (Apple) external peripherals do not include terminations.

6) you are allowed to leave all devices powered down *EXCEPT* the devices 
with attached terminations.

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).

Apple has a handy little book that comes with the SCSI cables: "Apple SCSI 
Cable System".  It contains all this info plus a lot more.

(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.)

Good luck.

---- Michael Teener -- 408-974-3521 ---------------------------------+
---- Internet teener@apple.com, AppleLink TEENER1                    |
---- Apple may know my opinions, but *I* am responsible for them     |
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