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INT
57h,
Function
1
-
Initialize
Disk Device
Entry:
AH
=
1
(function
code)
Exit:
AL =
Standard
BIOS
error
code
DS:SI
= Address
of
BPB
pointer array
CL
= Number
of
disks
This function
initializes
the disk device.
It
is
called
before the
first
access
to
the
disk.
It
is
also
used as a
disk reset function
when
an
error
occurs.
The
BPB
pointer
array
is
an
array
of
FAR
pointers,
one
for
each
supported
disk
drive.
The
size
of
the scratch buffer
passed
to
the Build
BPB
function
call
is
determined from
the
BPB's
passed
in
this
call.
The
buffer size
will
be
taken
as
the size of the largest sector size
returned
from
this
call.
INT 57h,
Function 2
-
Build
BPB
Entry:
AH
=
2
(function
code)
AL =
Drive
number
(starting
with
0)
DS:SI =
Address
of
scratch
buffer
CL
=
Media
descriptor byte
Exit:
AL =
Standard
BIOS
error
code
DS:SI
Pointer
to
new
BPB
The
scratch
buffer
is
available
for
whatever use
the
BIOS
may
require.
On
entry,
it
is
not
initialized.
The
size of the
buffer
is
determined from
the
default
BPB's
returned
from
function
1,
and
will
be as
large
as
the
largest
sector size
specified.
INT 57h, Function 3
-
Read
Sector(s)
Entry:
AH
=
3
(function
code)
AL
=
drive
number
(starting
with
0)
BL
=
Media
descriptor byte
CX
= number
of
sectors
to
read
DX
=
starting logical
sector
number
DS:SI =
starting
memory
address
Exit:
AL =
Standard
BIOS
error
code
12
-
data
error
14
-
write protect
(does
not
apply
to
read)
1
5
-
drive
not
ready
1
6
-
seek
error
17
-
sector
not
found
18
-
write
fault
(does
not apply
to
read)
OFFh
-
other
error
NOTE:
Read/Write
Sector(s) Functions:
The
FDD
circuit
is
automatically
powered
off
after
2 or 3
seconds
of
non-operation.
The Read
Sector(s)
and
Write Sector(s)
functions turn
on
the
power
of
FDD
circuit
and
its
motor
when
their
power
has
been
turned
off
automatically.
159
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