The difficulty with HP's nomenclature is the fact it hides a vital component.
 When one talks about FWSCSI on MPE, one is really talking about Fast Wide
Differential (AKA HVD High Voltage Differential) SCSI, as opposed to Fast Wide
Single-ended (AKA LVD or Low Voltage Differential)SCSI.  Single-ended SCSI is
HP's nomenclature for Fast Single-ended SCSI-2.  (BTW, the industry is moving
away from HVD and going to LVD.)

All this to say that if your DDS-4 drive is a Differential SCSI drive, you
should be able to connect it to the FWSCSI.  If it is not differential, DO NOT
CONNECT IT, its controller will get fried.

Think of differential SCSI as RS-422 and Single-ended SCSI as RS-232.
A differential controller generates a high voltage and the signal is the
difference between two pins.  A single-ended controller generates very little
voltage and the signal is the absence or present of the current on a pin.

So I went looking for some information at the HP site. (http://www.hp.com/ta
pe/datasheets/dat40.html#overview)

Unfortunately the DDS-4 drive listed there is LVD/SE Wide Ultra SCSI-2.  In
other words this device will not work on an HP e3000's FWSCSI controller,
without some sort of Differential to SE (LVD) converter.  Such devices exist.
 I have several here from Paralan (www.paralan.com.)  You could also connect it
to the SESCSI controller but you will probably need a 68 pin Micro-D to 50 pin
Micro-D cable with high-bit termination enabled.  You will also not get the
speed you should expect from a DDS-4.

Kind regards,

Denys. . .

Denys Beauchemin
HICOMP
(800) 323-8863  (281) 288-7438         Fax: (281) 355-6879
denys at hicomp.com                             www.hicomp.com


-----Original Message-----
From:   Neil Harvey [SMTP:[log in to unmask]]
Sent:   Friday, May 19, 2000 11:34 PM
To:     [log in to unmask]
Subject:        DDS-4 and SCSI

I've been following the thread on SCSI Babble with increasing confusion.

Is it possible to attach a DDS4 drive to a 9x9 (or 9x7, 9x8)?
Will it work on a "standard" FWSCSI bus?

TIA

Regards

Neil