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From: cameron@solaria.sol.net (Cameron Bicknell)
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Subject: SCSI tutorial / Hitachi CDR-1750S installation specs
Date: 17 Apr 1995 23:43:01 -0500
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*** SCSI information *** SCSI documentation ***  What you should know ***

Here is some information that anybody installing one of the Hitachi
CDR-1750S/CDR-1750SSN SCSI CD-ROM drives should know.  Most of the 
information contained applies to any SCSI installation.  Please retain a 
copy of this document if you purchased one of the Hitachi SCSI CD-ROM 
drives I am selling, or if you find the information to be useful.

The following is a detailed explanation of the functions of the switches
found on the back of the Hitachi SCSI CD-ROM drives.  Most other SCSI 
devices have either dip switches or jumper blocks for controlling these 
settings as well, so most of this information is universal.

Switch #1,#2,#3: SCSI ID - In most applications this should be set to an ID
of 2, 3, 4, 5, or 6.  This must never be set to 7 (reserved for the SCSI 
controller itself), and it is not recommended that it be set to 0 or 1 
(These are generally reserved as hard drive ID's).  Certain machines may
have other SCSI ID's that should not be used as well.  In any case, you
must NEVER set more than one SCSI device to the same ID.  This includes
the SCSI controller as well, which is considered a SCSI device.

Switch #4: Parity On/Off - This does not control parity of the SCSI
bus, it only contols whether or not the CD-ROM drive itself makes use of
the parity on the SCSI bus.  It is recommended that you have the parity
enabled on the SCSI bus (controlled by the SCSI controller), and whether
or not you enable the individual drives to make use of it is optional.
However, parity on the SCSI bus should only be enabled if all devices on
the SCSI bus support parity.  If you have any devices on the SCSI bus that
don't support parity at all, then you should not enable parity on the SCSI
bus (controlled by the SCSI controller), and then you should turn off 
parity on the remaining devices that have the parity option.

Switch #5: Terminator On/Off - Only the devices on the PHYSICAL ENDS of 
the SCSI bus should be terminated.  This has nothing to do with any of the
devices SCSI ID's.  If you ONLY use internal, or ONLY use external devices,
then the SCSI CONTROLLER should be terminated and the drive at the other
PHYSICAL END of the cabling should be terminated.  All other devices must
NOT be terminated.  However, if you use BOTH internal AND external devices,
that puts the SCSI controller in the MIDDLE of the SCSI bus, which means
that the SCSI controller MUST have termination DISABLED, and the device
physically at the end of the external cabling must be terminated, as well 
as the device physically at the end of the internal cabling must be 
terminated.  All other devices MUST NOT be terminated.  Many SCSI devices
and controllers make use of removable "terminator packs" that must be
physically removed to disable termination, or installed to enable 
termination.

Some devices as well as SCSI controllers have the option to enable or
disable "term power" or termination power to the SCSI bus.  This is not
the same as termination.  Termination power must be present on the SCSI
bus in order for termination to work as intended.  If your SCSI controller
is capable of supplying termination power to the SCSI bus and it is
enabled, then the drives are not required to provide it.  If the SCSI
controller is not capable of supplying termination power, or it is disabled
then the individual drives must supply it.  I have found that it usually
works best to enable term power on the SCSI controller.  You MUST enable
term power on the SCSI controller if the drives do not have the option of
supplying term power.  You may also allow SCSI devices as well as the
controller to supply term power at the same time.  I have found that in the 
case of long SCSI cabling or applications that have many drives connected 
that enabling the term power on the drives that support it as well as the 
SCSI controller will offer more reliable operation.  Termination power is
the reason why you must NEVER connect SCSI cables backwards or incorrectly.
If you do, you will blow a fuse on the controller or on one or more of the
SCSI devices connected to it.  Once the fuse is blown, term power will NOT
be supplied, and the SCSI bus will not operate properly until all blown
term power fuses are replaced.

Switch #6: Logical Block Length Selection - This is the MOST important
setting when installing a drive on a Sun Sparcstation.  There are two
options, 2048K and 512K block length.  The default is 2048K.  If the unit
is to be installed on a Sun or any other machine that uses 512K block
or sector size, you MUST change the setting to the 512K position.  If you
install a drive on a Sun or other 512K block machine, without setting the
drive to use 512K block size, it will NOT work.

The above information contains only the basics of SCSI configuration.
There may still be other settings that need to be configured in order to
make your particular installation work as desired.  Feel free to copy and 
distribute this information.  

Cameron Bicknell

(414)878-1419 <-- Voice phone number, evenings or weekends only please.

cameron@ide.mil.wi.us  <-- Preferred e-mail address.

cameron@solaria.sol.net  <-- Alternate e-mail address.

System Operator of Infinite Data Exchange BBS (414)878-2106 Racine Area
** These lines are for modem callers ONLY. ** (414)835-9931 Milwaukee Area