When a WRITE
PROTECT
switch is set
to
the
ON
position, the particular disk Is protected
from write operations regardless
of
any write commands which may be received. When a
WRITE
PROTECT
switch is set
to
the OFF position, write operations may then
be
executed.
The
PROT
indicators (Paragraph 3.14.5) Indicate the status
of
the protect switches.
3.15
03000 INTERFACING
The 03000 Interface is described in two sections: Controller (or Formatter) to Disk Drive,
and
Disk Drive
to
Controller (or Formatter).
The Interface is arranged such that as many
as
four different disk drives may be operated
on
the interface by a common controlier. This is accomplished by providing a group
of
(disk drive) Input lines and a group
of
output lines which become a common
I/O
bus. This
bus is time-shared by the various drives that may
be
connected with the bus, Le.,
daisy-chain arrangement.
3.16
INTERFACE INPUTS (CONTROLLER
TO
DISK
DRIVE)
All signal names are chosen to correspond
to
the logical true condition.
All
interface lines
are low-true at the interface with the low (true) condition considered
to
be
Ov,
and the high
(false) condition considered
to
be
+
3v.
3.16.1 UNIT SELECT LINES
There are four UNIT SELECT lines. A low level on one
of
these lines will connect one
pre-determlned disk drive
to
the common
1/0
bus.
The low level on these lines enables all
II 0 lines except:
(1)
BUSY
SEEKING (Paragraph 3.17.2)
(2)
MALFUNCTION
DETECTED
(Paragraph 3.17.10)
(3) ACTIVATE EMERGENCY UNLOAD (Paragraph 3.16.2)
(4)
START/STOP
DISK
DRIVE
(Paragraph 3.16.13)
These lines are enabled at
aI/ times. Thus,
it
can
be
seen that a unit must
be
selected to
determine
its
ready status but
it
is not necessary
to
select a unit to determine its busy
status.
When the Unit Number
Selector Switch Is included, the units are identified
to
switch
pOSitions and select lines on a one-terone basis, i.e., switch position 1, UNIT SELECT
NO.1 line, etc.
After a unit has been selected and the
1/0
bus has been allowed
2jJ.Sec
to
stabilize, the
selected disk unit will recognize inputs and provide stable outputs.
3.16.2 PLATTERSELECT
This
Is
a level which determines which platter is selected in dual platter models. When the
level on
this
line is low, the top (removable) platter is selected; when the level on this line
is high, the bottom (fixed) platter is selected,
as
shown in Table 3-1.
3.16.3 HEAD
SELECT
This is a level which determines which
head
and corresponding storage surface (top
or
bottom) is selected.
3-13
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