Adaptec GDTSETUP Bedienungsanleitung PDF herunterladen (Seite 38)

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In order to ensure a flawless and interference-free signal transmission on the SCSI bus and

to minimize the detrimental effects of external noise generators, both ends of the SCSI ca-

ble have to be terminated. The SCSI specification prescribes different termination methods

for SE and LVDS SCSI bus systems.

There are two alternative termination modes for Single-Ended SCSI bus systems: The pas-

sive termination and the active termination, also known as Alternative-2 termination. The

passive termination consists of a 220 Ohm pull-up and a 330 Ohm pull-down resistor for

each signal. Today, the passive termination is mostly used in systems with synchronous

data transfer rates not exceeding 5 MB/sec, which is rather slow. The active termination cir-

cuit consists of a 110 Ohm precision-resistor per signal and a common 2.85 Volt voltage

regulator. Thus, all signals are actively pulled up to a certain level. The active termination

provides much better signal quality and significantly reduced liability to noise.

LVDS SCSI bus systems allow only active LVDS termination. The termination circuitry must

automatically recognize, if the bus is operated in SE or LCDS mode and adjust itself ac-

cordingly.

All Wide/Ultra2 SCSI channels of the ICP Controllers are equipped with a LVDS compliant

termination. The additional Narrow/Ultra SCSI channel uses an active SCSI bus termina-

tion. The voltage for the termination circuitry is supplied either by the SCSI device itself, or

by the TERMPWR line(s) of the SCSI bus.

Most of the new Wide/Ultra2 SCSI devices are delivered without termination. I.e., the SCSI

bus cannot be terminated on the last device of the bus, but needs an external termination

which allows SE and LVDS operation (see B.4.4 "ICP SCSI Accessories").

 Always use active SCSI bus termination.

 Do not use SCSI devices with passive SCSI bus termination (e.g., CD-ROMs) for the ter-

mination of the SCSI cable.

 Always terminate only the two ends of a SCSI cable.

 The TERMPWR jumpers on the ICP Controller PCB should always be set.

With regard to a proper termination in SCSI configurations comprising of ICP Controllers,

SCSI devices, and SCSI cables, it is appropriate to go into further detail.

This already difficult topic is further complicated by the multi-connector systems of the ICP

Controllers. ICP provides on various models an internal standard 50 pin header, an internal

68 pin receptacle and an external 68 pin UHD connector. This is an enormous advantage of

ICP products; firstly, because you do not have to spend your money on expensive adapters,

second, because it offers you more connections. The only secure way of finding out which

particular connector to use and which terminator to enable is by analyzing the table below.

Note: To enable the option Auto, or toggle between the

and

OFF

termination settings

for a ICP Controller SCSI channel, use the Configure Controller menu in GDTSETUP.

The connections listed in the table below are the only valid connections allowed. Any other

connection setup, even if physically possible, is not allowed as it will cause serious mal-

functions or even the destruction of the SCSI devices and/or the ICP Controller.

1 2 ... 33 34 35 36 37 38 39 40 41 42 43 ... 217 218

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