ICP RS Series, Руководство пользователя, Страница: 40 / 193

40
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160MB/sec synchronous data transfer rate
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Up to 12 Meters cable length
It is very important for you to observe the information and notes given in this section of the
User’s Manual because it helps to ensure that the SCSI devices that are used in connection
with the ICP Controllers are operated in a successful, long-lasting and trouble-free manner.
In many cases, this information is not only applicable to ICP Controllers, but in general to
all those SCSI systems which, like the ICP Controllers, use Ultra160 SCSI technology. Ac-
cording to its definition, the SCSI bus provides access to several participants that are
physically connected through an appropriate SCSI bus cable. To achieve a sufficiently good
signal quality, it is not only recommended to use very good cables and connectors, but also
to terminate both ends of the cable properly. For an unambiguous identification on the
bus, all participants have a unique number – the so-called SCSI-ID. Further details on these
topics can be found on the following pages.
Please note that
98% of all SCSI-related problems are caused by bad SCSI cables,
wrong SCSI bus termination and duplicate SCSI-IDs.
B.4.1 SCSI Cables
The quality and overall length of the cable, as well as the number and quality of the SCSI
connectors is very important for both internal and external SCSI cables. Generally, internal
SCSI cables are 50 or 68 conductor flat ribbon cables. To connect external SCSI devices,
round and shielded cables with appropriate connectors are typically used. External round
cables should have a SCSI-compliant placement of the inside conductors and should be
approved for LVDS operation. Besides the cables, the right connectors for a cable are also
very important. It is highly recommend to use highest quality connectors, only.
The following table shows the maximum cable lengths allowed for a given transfer rate.
Based on many years of SCSI experience, the lengths we recommend are in some cases
shorter than theoretically possible. The information in the table refers to one SCSI channel
and represent the overall length of the cable, including internal and external parts.
SCSI Bus
Width SCSI Mode Bus-
Type
Synchronous
Data Transfer
Rate
Number of
devices
Max. Cable
Length
8 Bit, narrow Fast SE 10 MB/sec. 7 2.0 meters
8 Bit, narrow Fast-20, Ultra SE 20 MB/sec. 4 1.5 meters
8 Bit, narrow Fast-40, Ultra2 LVDS 40 MB/sec. 7 12 meters
16 Bit, wide Fast SE 20 MB/sec. 15 2.0 meters
16 Bit, wide Fast-20, Ultra SE 40 MB/sec. 4 1.5 meters
16 Bit, wide Fast-40, Ultra2 LVDS 80 MB/sec. 15 12 meters
16 Bit, wide Fast-80, Ultra160 LVDS 160 MB/sec. 15 12 meters
In addition to specifications mentioned above, the following should be kept in mind when
selecting and installing SCSI cables:
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Always install SCSI cables that are as short as possible. The lengths in the table above
are absolute maximum lengths. (Total length of internal and external cables per chan-
nel).
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Avoid using SCSI cables with more connectors than actually needed. Never select a SCSI
mode or operate a SCSI device with a cable that is not appropriate for this mode.