Installing The Host Adapter; Should You Change The Default Settings - Adaptec AHA-1520 User Manual

Chapter Two
Installing the Host Adapter
The Adaptec AHA-1520/1522 is easy to install into IBM PC/ AT and compatible
computers. This chapter gives you the information you need to install one or two
host adapters in your system. The chapter covers three major topics:
• how to terminate your SCSI bus
• how to decide whether you need to change the default settings of the
host adapter
• how to install the host adapter or adapters
WHICH SCSI DEVICES SHOULD BE TERMINATED?
For your system to operate properly, you must
tenninate
your SCSI bus correctly.
The SCSI devices at the physical beginning and end of the SCSI bus must have
terminators installed. All other SCSI devices on the SCSI bus must have their
terminators removed.
The AHA-1520/1522 is a SCSI device. If you are using only one of its connectors,
the host adapter is at one end of the SCSI bus. Its terminators should remain
installed. If you connect devices to both the external and internal connectors on
the host adapter, the host adapter is not at the end of the SCSI bus and its termina-
tors should be removed. Terminators should be installed on the SCSI devices on
both ends of the SCSI bus.
On the AHA-1520/1522 host adapters, terminators are single inline package (SIP)
resistors mounted on the board. Terminators on SCSI devices can take several
forms. They can be SIP resistors or they can be dual inline package (DIP) resis-
tors. Terminators on SCSI devices can also be set with switches. Consult the
documentation that came with your SCSI device to find out how to set its
terminators.
SHOULD YOU CHANGE THE DEFAULT SETTINGS?
The AHA-1520/1522 is set up at the factory to operate properly under most
circumstances. You need to make changes to the default settings of the board if
either of the following is true:
• You plan to use more than one AHA-1520/1522 host adapter in your
system.
AHA-1520/1522
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