Acer SmartRAID V Bedienungsanleitung PDF herunterladen (Seite 202)

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Theory of Operation

TERMPWR

SCSI terminators need power to operate. SmartRAID V controllers always

supply power for their own onboard SCSI terminators and, by default,

supply termination power for other devices using the TERMPWR line on

the SCSI cable. Most SCSI devices allow the way in which TERMPWR is

supplied to their onboard SCSI terminators to be selected using jumpers

on the device. Devices that supply SCSI bus termination should be

configured to supply their own isolated TERMPWR. This prevents loss of

receiver noise margin due to a DC voltage drop across the cable.

TERMPWR should remain enabled if there is a possibility of power-loss on

an external SCSI device that supplies its own TERMPWR.

If all devices supplying termination for the SCSI cable are also capable of

supplying their own termination power, then TERMPWR supplied to the

SCSI cable from SmartRAID V controllers can be disabled using SMOR or

Storage Manager.

SmartRAID V controllers supply termination power onto the SCSI cable

through a circuit breaker which protects the controller from a short-to-

ground on the TERMPWR line. Some SCSI devices use a fuse for

protection; this can require the replacement of the part if a short occurs or

if the SCSI cable is inserted incorrectly.

The ANSI XT3T9.3 SCSI-3 Parallel Interface working group recommends

that all TERMPWR lines be decoupled at each terminator to minimize

TERMPWR glitch coupling. The minimum recommended values are a

2.2µF solid tantalum capacitor along with .01µF ceramic capacitor in

parallel to suppress high frequency, low voltage noise. These capacitors

supply the high frequency, low impedance path to ground necessary to

provide a clean supply voltage.

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Acer SmartRAID V Bedienungsanleitung Seite 202