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[a]
t~~
f
[b)
Fig. 3.8 SCSI
termination
network
used with the
LS-10
scanner
Terminaison
interne
du LS-10
SCSI-AbschluB an Scanner LS-10
[c)
[d)
Fig. 3.9 SCSI internal
flat
cable
Cable en nappe SCSI interne
Internes SCSI-Flachkabel
46
[e)
3-4
Terminating
the SCSI Chain
The SCSI chain is an electrical bus connecting
two
or
more
devices
. It is
critical
that
this
bus be
correctly
terminated
for
the SCSI
peripherals
to
work
properly
.
Termination
is an
electronics
term
that
applies
to the
impedance found at both ends of the bus. The electrical
signals
on the SCSI bus
are
changing
rapidly
between
their
digital
" on" and
"off"
states. To
minimize
nOise, a
termination
is placed on each end of the bus. The effects
of this
termination
may be subtle, but
are
critical.
Typically, the
computer
sits at one end of the SCSI bus.
Assuming
this is the case, the SCSI
controller
in the
computer
has to be
terminated
.
Warnlngl
Incorrect
SCSI
termination
can
cau.e
unpredictable
error
•.
If one
other
SCSI
peripheral
shares
this SCSI bus, it
also
has to be terminated. If
additional
SCSI
devices
sit
on the bus between the
two
end SCSI devices, these
devices can NOT be
terminated
. Only
two
terminated
devices can
reside
on the SCSI bus, one
at
each end.
Improperly
terminated
SCSI
peripherals
can fail
immediately
or
may
work
correctly
for
a
week
before
generating
their
first
errors
.
Terminating
an LS-10
The
internal-mount
LS-10
scanner
uses a set of
termination
networks as seen in Figure 3.8. The pins of
these
term
ination networks
are
numbered
beginning
with
number
one. The
number
one pin is indicated with
a black dot.
[a]
SCSI
termination
off
[b)
SCSI
termination
on
3-5 SCSI Cables Used
with
Internal
Scanners
The internal SCSI cable is a 50-pin
flat
cable
with
two
identical stamped connectors on each end. One end of
this cable
will
connect to the SCSI
controller
while
the
other
end
will
connect to the
connector
on the
rear
of
the LS-10
scanner
. A typical SCSI internal
cable
is seen
in
Figure
3.9.
[c) SCSI flat
cable
[d)
SCSI 50-pin connectors
[e)
Connector protection key