Installation
23
Interface, cabling and connectors
The Viper 200 drives are available with LVD or HVD single-ended SCSI interfaces.
ANSI SCSI standards specify the technical requirements for correctly cabling and
connecting single-ended devices. This section provides some basic information
about SCSI cabling and connectors for the drives.
Notes:
•
HVD cannot be mixed with LVD or single ended devices.
•
The best performance can be attained in a system where all devices are
optimized for LVD SCSI, including drives, host and terminators.
•
The next best performance can be attained in single-ended mode with an LVD
host and terminator. If there is a single-ended device in the SCSI chain, the
drives will switch to the single-ended mode.
Interface summary
Viper drives conform to the ANSI SPI-2 (T10/1142D) standard. Compliance to this
standard is sometimes referred as Ultra2 SCSI. The LVD/SE Viper drives
(STU62001LW and STU42001LW) support single-ended (SE) and low voltage
differential (LVD). The HVD Viper drives (STU62001WD and STU42001WD)
supports high voltage differential (HVD) with 8- and 16-bit wide transfers.
LVD and HVD drives can be identified by the following labels, located above the
SCSI connector:
SCSI
LVD/SE
SCSI
DIFF
LVD label
HVD label
The drives typically operate on a daisy-chain interface in which other SCSI devices
are also operating. Devices on the daisy chain must all operate in the same mode,
either SE, LVD, or HVD but not a mixture of these. The LVD/SE model is LVD/SE
multimode compliant in that it automatically switches to LVD or SE as determined by
the level of the SCSI DIFFSENS line. Therefore any SE device on the daisy chain
forces the entire chain to SE mode. On the interface daisy chain, all signals are
common between all devices on the chain, or SCSI bus.
Caution:
An HVD drive should never be plugged into a SCSI bus that contains
LVD or SE devices.
The daisy chain of SCSI devices must be terminated at both ends with terminators of
the proper impedance, in order to operate correctly. Intermediate SCSI devices shall
not be terminated. Internal Viper drives do not have onboard termination circuits.
Some type of external termination circuits must be provided for these drives by the
end user or designers of the equipment into which the drives will be integrated.
