Seagate Barracuda 18XL ST318416N, Руководство по эксплуатации продукта

Страница: 89 / 110

Barracuda 18XL Product Manual, Rev. A 79
9.7 Electrical description
“LC” models use the single connection attachment (SCA) connector. This 80-pin connector is designed to plug
directly into a back panel or plane. No external cables are required. Active terminators on the back panel must
be provided by the user. This connector is not recommended where cabling is required.
“LC” and “LW” models are Multimode drives. That is, their I/O circuits can operate as either single-ended or low
voltage differential drivers/receivers (selectable using the I/O “DIFFSENS” line). They require external termina-
tors. See Section 9.7.2 for additional information on these models.
“N” and “W” models use single-ended interface signals. These signals must be terminated with 110-ohm active
termination circuits at each end of the total cable. Single-ended circuits use open collector or three state driv-
ers. These models can be configured to provide the SCSI termination.
Note. The SCSI protocol chip drives the upper eight data and parity bits of the SCSI bus even when operat-
ing in narrow (eight bit) mode. This is normal operation for this chip. If the unused data bit signals are
connected to conductors that extend out beyond this drive’s SCSI connector, correct termination must
be provided for these unused signals at the device/system at each end of the bus onto which this drive
is connected. Termination is required to control radiated emissions and conducted noise on other SCSI
bus signals.
9.7.1 Single-ended drivers/receivers
For “N” and “W” models which use single-ended drivers and receivers, typical circuits are shown in Figure 12.
Terminator circuits (Note [1]) are to be enabled only when the disc drive is first or last in the daisy-chain.
Transmitter characteristics
Single-ended drives use an ANSI SCSI compatible open collector single-ended driver. This driver is capable of
sinking a current of 48 mA with a low level output voltage of 0.4 volt.
Receiver characteristics
Single-ended drives use an ANSI SCSI single-ended receiver with hysteresis gate or equivalent as a line
receiver.
Figure 12. Single-ended transmitters and receivers on “N” and “W” models
Notes.
[1] Part of active terminator circuits. Non-removable LSI terminators, enabled in the drive (models “N” and
“W” only) with jumper plug TE when it is first of last in the daisy-chain.
[2] ANSI SCSI compatible circuits.
[3] Total interface cable length should not exceed that specified in ANSI Standard T10/1302D.
[4] Source of drive terminator power is an active circuit which has an input source voltage selected by jumper
plug TP. See Figure 7d. Applies to “N” and “W” models.
[5] Interface signal levels and logical sense at the drive I/O connector for “N” and “W” models are defined as
follows:
Vil (low-level input voltage) = 1.0 V maximum (signal true); minimum = Vss – 0.5 V.
Vih (high-level input voltage) = 1.9 V minimum (signal false); maximum = Vdd +0.5V.
Vihys (Input Hysteresis) = 425 mV minimum
Transmitter
(or transceiver)
Line Driver
Flat
Cable
Pair
[3]
[5]
[2]
[4]
[1]
110
Ohm
[4]
[1]
110
Ohm
Receiver
Line Receiver
[2]
TP TP