A-48
HP 9895A
Disc
Memory Command Set
Format
Type:
Purpose:
Descri pti on:
Disc write.
The
Format
command
is
a
part
of
the
sequence
of com-
mands
which
changes
a disc which is unformatted
or
has
the
wrong format into a disc with a usable format.
The
9895A supports
three
types of formats: HP
double
de-
nsity, single-
or
double-sided
and
Single-sided
standard
IBM
format disc.
The
formatting operation also
can
make
tracks marked with
the
D bit into invisible tracks.
The
format
sequence
was designed to allow
the
disc con-
troller to
do
as much of
the
work of formatting as possible,
but
still allow
the
host system to set its own criteria for:
1. Format type,
2. Bad track detection,
3.
Sector
interleave,
4. Spiral offset,
5. Format
data
byte.
After receiving
the
Format
command,
parallel poll is dis-
abled
and
the status of
the
specified unit
is
checked.
If
the
unit
can
be
used,
the
disc is formatted according
to
the
type, old format override, interleave
and
selected
data
byte.
If
the
disc
is
of a different format
than
the
Format com-
mand
requests
or
the
override old format bit
is
set,
the
entire disc
will
be
formatted without invisible tracks.
If
the
disc
is
the
same
type as
that
requested
by
the
Format
command
and
the
override old format bit is
not
set, 9895A
will
attempt
to
read
from
each
track before it is formatted
and
make
that
track invisible if:
1.
The
track
is
already invisible,
2. A sector with a D bit
set
is found,
3.
The
track
has
no
readable sectors.
NOTE
The 9895A looks at the D bit
of
a random sector to decide whether
or not to make that track invisible.
HP format requires that the D
bit
of
all
the sectors be set so there
is
no problem. But,
IBM
format
allows a mixture of set and cleared D bits on one track. Therefore,
before formatting an
IBM
disc,
all
D bits on a good track should be
cleared and
all
D bits on a bad track set.
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