Chapter 6. Theory of Operation
EK–MOL80–SV. B01
6–37
Finally, SCSI is capable of high data transfer rates. Synchronous data transfer
rates may be as fast as 4 Mbytes/second, and asynchronous rates up to 1.5
Mbytes/second, limited only by the capabilities of the computer and peripheral.
CAUTION
DO NOT CYCLE POWER during any
troubleshooting until you are sure the system
SCSI bus is INACTIVE and will REMAIN
INACTIVE.
Removing power while the bus is active can
cause data loss and/or indeterminate bus
states. Check the host system reference
manuals for information on checking the
status of the SCSI bus.
Single-Ended and Differential SCSI Interfaces
The SCSI interface on this jukebox accepts either single-ended or differential
SCSI buses.
Internally, the jukebox is a single-ended interface. A single-ended
external connection is repeated onto the jukebox bus. A differential external
connection is converted into the internal single-ended bus (and also repeated).
Because the single-ended interface is repeated onto the internal bus, maximum
external bus length remains at the maximum SCSI single-ended bus length of 6
meters. Even though the differential bus is also repeated as it is converted, prop-
agation delays require shortening the maximum differential SCSI external bus
available (25 meters) by 10 meters. This leaves a maximum of 15 meters
available.
A single-ended SCSI interface may be preferable when peripherals are physically
close to the host and short SCSI cables are adequate to connect (or daisy chain)
them.
An example of an appropriate use of a single-ended SCSI interface is when
a host and several peripherals are daisy-chained and located in an upright cabinet
with 1-meter cables connecting them.
A differential SCSI interface is used when up to 15 meters of SCSI cabling is
needed, and the peripherals need to be physically located farther apart than the
single-ended SCSI interface allows.
An example of an appropriate use of a
differential SCSI interface is when a peripheral must be located in a different
location than the host system for security reasons or for user convenience.
