Terminator Requirements; Figure 25. Typical Se-Lvd Alternative Transmitter Receiver Circuits - Seagate ST34520N - Medalist 4.55 GB Hard Drive Product Manual

Medalist Pro Product Manual, Rev. D
Figure 25. Typical SE-LVD alternative transmitter receiver circuits
9.8

Terminator requirements

Internal disc drive I/O termination (provided only in model "N" and "W" drives single ended I/O model drives)
consists of active circuits in an LSI module that is permanently mounted on the PCB. All single initiator/single
target (non-daisy-chain) applications require that the Initiator and disc drive be terminated. Daisy-chain appli-
cations require that only the units at each end of the daisy-chain be terminated. All other peripherals on the
chain must not be terminated. (See Figure 19).
Note. Remove drive terminator enabling jumper TE where terminators are not required. Removal of termina-
tor power source selection jumper TP (see Figure 7d) does not disconnect the terminator resistors
from the circuit.
It is highly recommended that ANSI SCSI-2 Standard's Alternative 2 termination (active termination) be used
for applications with single-ended ("N" and "W" models), especially if the bus will be operated at transfer rates
above 5 Mbytes/sec. The "N" and "W" models provide on-board active termination that can be disabled by
removal of the enable jumper TE (see Figure 7d).
Note. ACTIVE TERMINATORS ARE HIGHLY RECOMMENDED FOR USE IN THE DAISY-CHAIN AS
DESCRIBED ABOVE. ACTIVE AND PASSIVE TERMINATORS SHOULD NOT BE MIXED ON THE
SAME SCSI BUS.
Drive models "WC," "LW," and "LC" do not have internal terminators available. The user, systems integrator or
host equipment manufacturer must provide a terminator arrangement external to the drive. For "LW" models,
terminator modules can be purchased that plug between the SCSI I/O cable and the drive I/O connector or on
the end of a short I/O cable stub extending past the last cable connector.
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.
ANSI Standard X3T10/1143D contains additional details about SCSI bus terminator and terminator power
requirements.
VCCA
LVD Signal Drivers
Single
Ended
Circuitry
Receiver
Single
Ended
Ground
Driver
LVD Signal Drivers
Ground
Single Ended: GND
LVD: +Signal
VCCB
Single
Ended
Receiver
LVD
–Signal
–Signal
Single
Ended
Negation
Driver
Single
Ended
Assertion
Driver
73