Electrical Description - Seagate ST32430N - Hawk 2.1 GB Hard Drive Product Manual

Product Manual - Hawk 2LP Family SCSI-2 (Volume 1), Rev. A
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11.6.4

Electrical description

Model "N" drives use single ended interface signals. These signals must be terminated with 110 ohm active
termination circuits at each end of the total cable. On "N" models, the terminators are enabled (or disabled) by
installing (or removing) jumper plug TE. See Figure 10.1-1. Single Ended circuits use open collector or three
state drivers. See Figure 11.6.4-1 and 11.6-1. The model NC has no provisions for terminators on the drive.
The "ND" model drives use differential interface signals and each of these must be terminated at each end of
the total cable with 330 ohms to +5 V and 330 ohms to ground with 150 ohms between each differential pair.
All I/O circuits are open collector, three state drivers. See Figure 11.6.4-2 for circuit drawing. Differential I/O
drives are shipped without terminators. These drives have no provisions for adding terminator sockets on the
PCB. On these drives some method of external termination must be provided by the drive user, systems
integrator or host equipment manufacturer.
11.6.4.1 Single ended drivers/receivers
For "N" models which use single ended drivers and receivers, typical circuits are shown in Figure 11.6.4-1.
Terminator circuits (Note [1]) are to be enabled (model N) 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.
[1] Part of active terminator circuits. Non-removable LSI terminators, enabled in the drive (model "N" only) with
jumper plug TE when it is first of last in the daisy-chain. Interface signals levels and logical sense at the
drive I/O connector are defined as follows:
Logic Level
NEGATED (0)
ASSERTED (1)
The difference in the voltages between input and output signals is due to the losses in the cable.
[2] ANSI SCSI compatible circuits
[3] Total interface cable length should not exceed that specified in Section 11.6.2.2.1.
[4] Source of drive terminator power is an active circuit which has an input source voltage selected by jumper
plug TP. See Figure 10.1-1. Applies to model "N" only.
Figure 11.6.4-1. Single ended transmitters and receivers
Line Driver
TP
Transmitter
[4]
(or transceiver)
110
[1]
Ohm
[3]
[2]
Driver Output
>2.5 V: <5.25 V
<0.4 V: >0.0 V
Line Receiver
TP
Receiver
[4]
Flat
110
Cable
[1]
Ohm
Pair
[2]
Receiver Input
>2.0 V: <5.25 V
<0.8 V: >0. 0 V
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