Eagle 450 Upgrade Instructions, Rev. A00
Appendix A - SCSI Termination
SCSI TERMINATION USING EXTERNAL TERMINATOR
The preferred method of terminating the SCSI bus in an AMOS based computer is the installation of an
external terminator. In April 1993, the external SCSI bus terminator became standard on all AMOS
computers. Using an external terminator makes installing an add-on subsystem (like a portable CD-ROM
drive) easier, eliminating the need to remove terminators from a SCSI device located in the host
computer. In the Eagle 450, the external terminator must be an “active” terminator. Do not continue to
use the passive terminator from your earlier system after you upgrade to the Eagle 450.
The SCSI bus must be terminated at each end of the cable. The AM-138 terminates one end of the bus.
The other end must be terminated by an active external terminator. An active terminator for the SCSI bus
you ordered—either narrow (PRA-00222-21) or Wide (PRA-00222-20)—is included in your Eagle 450
upgrade kit.
The AM-138 board is sensitive to incorrect SCSI bus termination. If you are using the external
terminator and one of the SCSI devices inside the computer also has its terminators installed, you
will experience problems.
To use the external terminator, make sure none of the SCSI peripherals inside the computer are
terminated. The termination power for the SCSI bus is provided by the AM-138 board.
An external narrow terminator is shown in Figure A-1:
SCSI
(PRA-00222-21)
EXTERNAL SCSI BUS
ACTIVE TERMINATOR
BAIL LOCKS
NARROW SCSI TERMINATOR
Figure A-1: Active External Terminator Installation
