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1.18.2
Drive Select
As shipped from the factory, the disk drive
is
configured to operate in a single-drive system. The user can easily
modify
it
to operate with other drives in a multiplexed, multiple-drive system. The user can activate the multiplex
option by cutting the MX
position
of the programmable
shunt,
located at IC location 1 E, which allows the input/
output (1/0) lines to be
multiplexed.
The Select lines provide a means of
selecting
and deselecting a disk drive. These four (4) lines- NDS0 through
NDS3
-
select one of the four
(4)
disk drives attached to the controller.
When
the
signal
logic level is
true
(low), the
disk drive electronics are activated and the disk drive
is
conditioned to
respond
to Step or
to Read/Write
commands.
When the signal
logic
level is false (high), the Input Control lines
and the Output Status
lines
are disabled.
A Select
line
must
remain
stable
in the true (low)
state until
the
execution
of a Step or Read/Write command is
completed.
The disk
drive address
is determined
by a Select Shunt on the PCBA. Select lines zero-through-three (0-3) pro-
vide a means
of daisy chaining a maximum of four
(4) disk drives
to a controller. Only one (1) line can be true (low)
at a time. An undefined
operation
might result if
two or more units are assigned the same address or if two or more
Select
lines
are in the true (low)
state simultaneously
(see
Figure 1-6).
The
Program
Shunt
is AMP
Part
Number 435704-7. The Program Shunt positions can be cut using AMP's Part
Number
435705. The Program
Shunt
is installed in
a dip socket. At the user's option, the Program Shunt may be
removed
and replaced
by a dip switch.
In
addition, the
user
may choose to have the Program Shunts prepro-
grammed and/or
color coded
by AMP. For this
service, contact your local AMP representative.
1.19
POWER SAVE OPTION
As
shipped from
the
factory,
the disk drive
is
configured to operate in a single-drive system. Jumper (0 ohm resis-
tor) R51 maintains the
power
to
the stepper motor whether or not the disk drive is selected. However, the jumper
in
position R51
may
be moved
to
position RS0. RS0 removes the power to the stepper motor when the disk drive is
not selected, for
a savings approximately equal to 3.8 watts per drive. When RS0 is used, at the time the disk drive
is reselected
,
the
user
must
ensure
the track location.
1-14
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