1540 and sync. SCSI drives

[neese at adaptex.UUCP]

Whether or not the 1540 negotiates for synchronous transfers is dependent
on the device and the state of the J1.1 jumper on the 1540.  If the J1.1
jumper is installed, the 1540 will negotiate for synchronous transfer
protocol, if the J1.1 jumper is not installed, it is then up to the device
to negotiate for synchronous protocol.  Only one device I know of negotiate
for synchronous protocol and it is the HP line of SCSI drives.  The 1540
will support a mix of protocols.  If one drive will not support synchronous
and the other drive will, then the 1540 will use the correct protocol for
both drives.
This would lead one to believe that the J1.1 jumper should be installed
by default, if the HP drives are the only ones that will do the synchronous
negotiation.  This would be great if all devices were really SCSI compatible.
(Sigh)  There are some devices that will go into the ozone if an extended
message is sent to the device that the device doesn't support.  When this
happens the device is supposed to simply reject the message and go about it's
business.  But this is not the case in all devices.  The Toshiba CD-ROM will
lose its mind when a synchronous message is sent to it.  Some of the early
SCSI drives will do the same thing.
But most of the newer SCSI hard drives will work correctly, and most of them
support synchronous protocol.  You'll know reall quick if the device you have
does not support it correctly.  Nothing will happen (including boot).  If the
drive you have does support synchronous, then you shouild have the J1.1 jumper
installed (unless it is an HP drive).  This will yeild about 30% higher
throughput.


			Roy Neese
			Adaptec Central Field Applications Engineer
			UUCP @ {texbell,attctc}!cpe!adaptex!neese
				merch!adaptex!neese