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Hardware Installation
AHA-1510A/20A Series User’s Guide
Stock Number: 510400-00, Rev. C Page: 3-7
Print Spec Number: 491842-00
Current Date: 11/18/94 ECN Date: 11/29/94
Connecting SCSI Devices
SCSI devices are connected by cables in one continuous line called
the SCSI bus. Each host adapter on the AHA-1510A/20A imple-
ments a separate SCSI bus, supporting up to seven 8-bit devices.
AHA-1510A/20A Series host adapters have an internal and external
SCSI connector to which you can attach up to seven SCSI devices.
This section explains how to connect both internal and external SCSI
devices to the host adapter connectors.
Caution: AHA-1510A/20A host adapters support
only single-ended SCSI devices. Differential SCSI
devices may be damaged if you connect them to the
host adapter bus. Most SCSI devices are single-
ended. Read your SCSI device documentation if you
are not sure whether a device is single-ended or dif-
ferential.
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
especially 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 80-110 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, which
you can purchase by calling Adaptec at the number listed on page ii.
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 synchro-
nous data transfer rates
■ 3 meters (9.8 feet) if you are using Fast SCSI data transfer rates