Adaptec AHA-2742T User Manual - Page 31

The Host Adapter and the SCSI Bus

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AHA-2740 Series User's Manual The Host Adapter and the SCSI Bus The AHA-2740 Series acts on your computer's behalf as the host to your suite of SCSI devices. Each chain of SCSI peripheral devices and their host adapter work together, and is referred to as a SCSI bus. When connecting SCSI devices to the SCSI bus, consider the following: • Each AHA-2740/2742 installed in your system can be used to form a SCSI bus consisting of up to seven internal and external SCSI devices on its single-channel (SCSI Channel A). • Each AHA-2740T/2742T installed in your system can be used to form two SCSI busses using its TwinChannel architecture (SCSI Channel A and SCSI Channel B). SCSI Channel A can control up to seven internal and external SCSI devices, while SCSI Channel B can control up to seven internal SCSI devices only. • The number of host adapters installed in your system is limited only by the number of available EISA slots that support bus master functions. • As with any standard bus, the wires in a SCSI cable resemble transmission lines which can generate undesirable effects such as, signal reflection and uneven loading of the line drivers. To reduce these effects, the SCSI bus must be properly terminated. (Termination on the SCSI bus is discussed in detail later in this chapter.) • To identify each SCSI device's address, and to determine its priority on the SCSI bus, each SCSI device (including the host adapter) located on the SCSI bus must be set to a unique SCSI ID (0-7). (SCSI ID setting is discussed in detail later in this chapter.) 2-4 Adaptec AHA-2740 Series User's Manual Stock Number: 510381-00 / Rev. C (Page 2-4) Print Spec Number: 491709-00 Rev C Current Date: 9/1/93 ECN Date: 9/14/93

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The Host Adapter and the SCSI Bus
The AHA-2740 Series acts on your computer’s behalf as the host
to your suite of SCSI devices. Each chain of SCSI peripheral
devices and their host adapter work together, and is referred to
as a SCSI bus. When connecting SCSI devices to the SCSI bus,
consider the following:
•
Each AHA-2740/2742 installed in your system can be
used to form a SCSI bus consisting of up to seven internal
and external SCSI devices on its single-channel (SCSI
Channel A).
•
Each AHA-2740T/2742T installed in your system can be
used to form two SCSI busses using its TwinChannel
architecture (SCSI Channel A and SCSI Channel B).
SCSI Channel A can control up to seven internal and
external SCSI devices, while SCSI Channel B can control
up to seven internal SCSI devices only.
•
The number of host adapters installed in your system is
limited only by the number of available EISA slots that
support bus master functions.
•
As with any standard bus, the wires in a SCSI cable
resemble transmission lines which can generate undesir-
able effects such as, signal reflection and uneven loading
of the line drivers. To reduce these effects, the SCSI bus
must be properly terminated. (Termination on the SCSI
bus is discussed in detail later in this chapter.)
•
To identify each SCSI device’s address, and to determine
its priority on the SCSI bus, each SCSI device (including
the host adapter) located on the SCSI bus must be set to a
unique SCSI ID (0-7). (SCSI ID setting is discussed in
detail later in this chapter.)
Adaptec AHA-2740 Series User’s Manual
Stock Number:
510381-00
/
Rev. C
(Page 2-4)
Print Spec Number:
491709-00 Rev C
Current Date:
9/1/93
ECN Date:
9/14/93
AHA-2740 Series User’s Manual
2-4