Electrical Description; Single-Ended Drivers/Receivers; Figure 12. Single-Ended Transmitters And Receivers - Seagate ST118273N Product Manual

Barracuda 18 Product Manual, Rev. C
9.7

Electrical description

"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.
The "WD" model uses high-voltage (HVD) differential interface signals and each of these must be terminated at
each end of the total cable with 330 ohms to +5V and 330 ohms to ground with 150 ohms between each differ-
ential pair. All I/O circuits are open collector, three state drivers. These HVD I/O drives are shipped without ter-
minators. These drives have no provisions for adding terminator sockets on the PCB. This means some
method of external termination must be provided by the user when termination is required.
"WC" and "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 9.7.2.2 for additional information on these models.
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.
See ANSI Standard X3T10/1142D for detailed electrical specifications.
9.7.1

Single-ended drivers/receivers

For "N," "W," and "WC" models which use single-ended drivers and receivers, typical circuits are shown in Fig-
ure 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.
Line Driver
Transmitter
(or transceiver)
[2]
Figure 12. Single-ended transmitters and receivers
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.
TP
[4]
Flat
110
Cable
[1]
Ohm
Pair
[5]
[3]
Line Receiver
TP
Receiver
[4]
110
[1]
Ohm
[2]
67