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[a]
[b)
Fig.
2.4
SCSI termination on the rear of the LS-10E
scanner
20
Terminaison SCSI iI I'arriere du scanner
LS-10E
SCSI-AbschluB an der Ruckseite des
Scanners LS-10E
2-3
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
terminator is placed at each end of the bus
.
The effects
of
this
termination may be subtle, but are critical.
Warnlngl
Incorrect SCSI termination can cause unpredictable
errors.
Typically,
the
computer sits as one end of the SCSI
bus.
Assuming this is the case, the SCSI controller
in the
computer has to be terminated
.
If another SCSI peripheral shares this SCSI bus,
it
also
has
to
be terminated
.
If additional SCSI devices sit on
the bus in 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.
Terminating an LS-10E
The LS-10E scanner box is configured with two 50-pin
SCSI connectors on the rear of the
LS-10E
unit as shown
in
Figure 2.4. Install the standard 50-pin SCSI terminator
onto the bottom connector
if
termination is desired. If
the LS-10E sits
in
the center of a SCSI chain
,
then by
necessity,
the bottom connector will be used for a SCSI
terminator.
[a]
SCSI connectors
[b] TERM
.
PWR. switch
[c]
SCSI terminator
Term. Power Switch
If the terminator-power
is
supplied by the other
connected
peripherals,
always turn off the
"
TERM
.
PWR
"
switch on the
rear
panel.
If
it is
not so supplied
,
always turn on the switch
.
ON
:
Supplies SCSI terminator-power
OFF: Stops supplying SCSI terminator-power
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