When the
WRITE
ENABLE line Is placed in the high state (any low
to
high change
of
state),
the erase current must remain
enabled for a period
of
time thereafter; the minimum time Is
defined
as
the minimum erase gap time. (The erase current may remain enabled for a
period
of
time greater than the minimum erase gap time.)
3.16.9
WRITE DATA SIGNAL
The
bit-serial write data pulses on this line control the switching
of
write current in the
magnetic head. The write electronics must
be conditioned for writing.
For each high to
low transition
on
the
WRITE
DATA
SIGNAL line, a flux change will
be
produced at the write
head
gap. This will cause a flux change to
be
stored on the selected
disk
surface~
The data and clock form the combined write data signal
and
the double frequency method
of phase mode encoding is used. The repetition rate
of
the high
to
low transitions when
writing all zeros is equal to the nominal data rate
~O.25
percent. The repetition rate
of
the
high to
low transitions when writing all ones is equal
to
twice the nominal data rate ±O.25
percent.
NOTE
It
is recommended that the
WRITE
DATA
SIGNAL be
turned
off
when performing a READ operation.
3.16.10
READ
ENABLE
This
is
a level which, when low
and
the unit Is selected and ready, enables the outputs
from the
read
electronics, i.e.,
READ
DATA
and
READ
CLOCK.
When this line Is low, the
read
electronics must detect one clock transition before any
clock and data pulses may
be transmitted, i.e., the first clock transition
of
preamble or gap
will not
be transmitted but all others will
be
transmitted assuming the required conditions
are
met. This arrangement prevents pulses
of
less than normal duration from being
transmitted.
When the
READ
ENABLE line is high, the
read
electronics outputs are Immediately
disabled and,
if
any data or clock pulses
are
In
progress, these pulses will
be
shaved.
NOTE
It
is recommended that the control/er
be
designed such
that the low to high transition
of
READ ENABLE is timed
or caused
by
a clock pulse transition.
3.16.11
TRACKOFFSET
The TRACK OFFSET
PLUS
line
and
the TRACK OFFSET MINUS line provide a means of
margin testing.
When one
of
these lines is low
and
the unit is selected and ready, the heads are slightly
offset from the normal track center. The direction
of
the offset is determined by the active
line. A plus direction is defined as being toward the disk center; a minus direction is
defined
as
being away from the disk center. Table
3-2
defines the operational condition of
the disk drive when the track offset function is used.
3-16
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