Re: Help with Zip Drive and the IIgs

[dempson@actrix.gen.nz (David Empson)]

EDavis <LNUSMNF.EDAVIS02@eds.com> wrote:

> More clarification:
> 
> I have an Apple SCSI card.  I have the Syquest drive with a SCSI ID of
> "4", and the Zip is using "5".
> 
> I see that the SCSI card has 4 dip switches, and I don't remember
> setting these up when I got the card (circa '90).

Given that there are four DIP switches on the card, you must be using
the Apple High-Speed SCSI card, not the original one.  This is good,
because there can be problems using removable SCSI devices (such as the
SyQuest and ZIP) with the original Apple SCSI card.

The first DIP switch selects whether DMA is enabled.  The other three
set the SCSI ID of the card.  The card is shipped with the SCSI ID set
to 7, and it is very unlikely that you would ever need to change this.

> Could the dip switches need to be set a specific, DIFFERENT way to have
> more than one drive attached???

Only if there was a SCSI ID conflict with a newly connected device, and
that is very unlikely.

> If I have only the Zip drive attached to the Apple SCSI card, turn the
> termination switch to "on" at the back of the Zip, it is at least 
> recognized by the IIgs.  I can boot from the 3.5" drive, and get asked
> if I want to initialize the disk.  I have said "yes" in the past.  As
> the Finder comes up, it repeatedly tells me that I already have a disk
> with the name z1 on the desk top, and I need to rename the disk to a
> suggested z11.  Then a z12, and so on, until my desktop is full of
> renamed Zip volumes.

This is not going to work.  For SCSI busses to work properly, they need
to be terminated correctly, and something needs to be providing power
for the termination.

The Apple SCSI cards do NOT provide termination power unless they are
modified to do this.  Neither does a ZIP drive.  Your SyQuest drive
_might_ be able to provide termination power, and I suspect it can,
given that you were able to use it without problems.

I suggest arranging your SCSI bus as follows:

Computer ---- ZIP ---- SyQuest

Make sure SCSI termination is OFF for the ZIP.  If you have an external
SCSI terminator, it must be connected after the SyQuest.  Also make sure
that the SyQuest and ZIP have different SCSI IDs (the ZIP is either 5 or
6, so the SyQuest can be anything from 0 to 4 without possibility of
causing a conflict).  The highest numbered device will be your boot
device.


As far as correct termination is concerned: with an Apple High-Speed
SCSI card, this means that the last device in the SCSI chain must be
terminated.  The SCSI bus requires termination at both ends.  The card
itself has termination for the computer end, so you just need
termination at the other end.  Internal termination on any device in the
middle of the chain must be disabled.  (For most devices this means
opening it up and pulling out resistors, or changing a jumper or DIP
switch for newer devices with "active termination".)

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand