Connecting Scsi Cables And Devices; Choosing Scsi Cables; Maximum Cable Lengths; Stock Number: 510600-00, Rev. A Page - Adaptec AHA-3940 User Manual

Connecting SCSI Cables and Devices

Choosing SCSI Cables

Always use high-quality SCSI cables to connect the host adapter to
devices on the SCSI bus. Poor-quality cables can cause data corrup-
tion, parity errors, and other problems. High-quality cabling is espe-
cially critical if you use Fast SCSI data transfer rates.
The round cables used for external SCSI devices vary widely in
quality and electrical characteristics. Be sure that external SCSI
cables meet SCSI-2 standards (your cable vendor can tell you this).
Here are some guidelines for external SCSI cables:
Use cables with a single-ended impedance range of 80-132
ohms.
Do not use cables shorter than 30 cm (11.8 inches) between any
two SCSI devices.
Adaptec sells high-quality internal and external SCSI-2 cables and
16-bit Wide SCSI cables. If your reseller does not stock these cables,
call Adaptec directly at the number listed on page iii.

Maximum Cable Lengths

To assure reliable operation, the total length of the SCSI bus, includ-
ing both internal and external cabling, should not exceed 6 meters
(19.7 feet) if you are using asynchronous or synchronous data trans-
fer rates, and 3 meters (9.8 feet) if you are using Fast SCSI data trans-
fer rates.
Caution:
AHA-3940/3940W host adapters support only
single-ended SCSI devices. Differential SCSI devices may be
damaged if you connect them to the SCSI bus. Read your
SCSI device documentation if you are not sure whether a
device is single-ended or differential.
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AHA-3940/3940W User's Guide
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Stock Number: 510600-00, Rev. A
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Print Spec Number: 492707-00

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Current Date: 8/24/94

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Installing Your Host Adapter and SCSI Devices
Page: 2-7
ECN Date: 08/30/94
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