Product manual

70 Barracuda 2LP Product Manual, Rev. D
11.7.1 Physical characteristics
This section defines the connectors, cables, signals, and terminators
needed to implement the SCSI interface.
11.7.1.1 Physical description
You can daisy chain multiple SCSI devices on a common cable if each device
has the same type of drivers and receivers (all single-ended or all differen-
tial). Devices having single-ended interface circuits cannot be on the same
daisy chain with devices having a differential interface circuit. Both ends of
the cable must be terminated. All signals are common between SCSI
devices. A maximum of 8 SCSI devices (including the host) may be daisy
chained together when using a non-wide bus and ST31250N/ND or
ST32550N/ND drives. A maximum of 16 SCSI devices (including the host)
may be daisy chained together when using a wide bus and ST31250W/WD/
WC/DC or ST32550W/WD/WC/DC drives.
Terminate both ends of the daisy chain, but do not terminate any interme-
diate SCSI device. The single-ended (ST31250N, ST31250W, ST31250WC,
ST32550N, ST32550W, and ST32550WC) drives are equipped with perma-
nently mounted IC terminators, which you can turn on or off using the Enable
SCSI Terminator jumper. See Section 10.1 to locate the Enable SCSI
Terminator jumper for each drive model. The differential (ST31250ND,
ST31250WD, ST31250DC, ST32550ND, ST32550WD, and ST32550DC)
drives do not have on-board terminators.
11.7.1.2 Cable requirements
Sections 11.7.1.2.1, 11.7.1.2.2, and 11.7.1.2.3 describe the single-ended,
differential, and general cable requirements for Barracuda 2LP drives.
11.7.1.2.1 Single-ended I/O circuits (ST31250N, ST31250W, ST31250WC,
ST32550N, ST32550W, and ST32550WC drives)
The maximum total cable length for use with drives having single-ended I/
O driver and receiver circuits is 6 meters (19.7 feet) when operating at line
data transfer rates of 5 Mbytes/second or less, and 3 meters (9.85 feet)
when operating at transfer rates greater than 5 Mbytes/second (fast SCSI).
A stub length of no more than 0.1 meter (0.33 feet) is allowed off the mainline
interconnection with any connected equipment. An ideal impedance match
with cable terminators implies a cable characteristic impedance of 132
ohms. Single-ended I/O cable pin assignments for ST31250N and ST32550N
drives are shown in Table 17. Single-ended I/O cable pin assignments for
ST31250W and ST32550W drives are shown in Table 19. Single-ended pin
assignments for ST31250WC and ST32550WC drives are shown in Table
21. ST31250WC and ST32550WC drives do not use I/O cables; they are
designed to plug directly into a back-panel connector.
11.7.1.2.2 Differential I/O circuits (ST31250ND, ST31250WD, ST31250DC,
ST32550ND, ST32550WD, and ST32550DC drives)
The maximum total cable length for use with drives having differential I/O
drivers and receiver circuits is 25 meters (82 feet). A stub length of no more
than 0.2 meter (0.66 foot) is allowed off the mainline interconnection with any
connected equipment. An ideal impedance match with cable terminators