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INPUT/OUTPUT FUNCTIONS
EXIT CONDITIONS:
25.3 -- Device Independent I/O Functions
properly reserved and
opened
Ci. e. ,
no
e~rors
occurred)
via the .RESRV
and . OPEN functions,
respectively.
lOCDTT
must have the "S" bit set
to
one
(sector
I/OL
The
mode
flag
(bit
"M")
must
specify either the input or
the
update
modes as configured prior
to
opening
the file.
IOCLSN
must contain. the
logical
sector
numbe-r
that
is
to
be
read.
The
actual number
Or
sectors read
depends
on the size
Or
the sector buffer
(see
beloUi).
The
data sectcl"s
of the
rile
begin
with
logical sector zero.
If
the
RIB
is to
be
accessed
via
the
.GETLS
function,
then
IOCLSN
must
contain the value $FFFF.
IOCSBS
must contain
the
starting
address
of
a
sector
bufTer.
The
sector
buffer must be an integral number
of
sectors
in
size
(see
section
25.3. L 20).
Th
is
buffer
does
not
necessarily
have
to
be
the
same one
used to open the
rile.
The
sector
buffer can
be in
a different location
for· each.
GETLS
callj
houseverl
if the
sector
buffer
is
to be
moved
after
a
rile has been
opened,
then
IOCSBS,
rOeSBE,
and
rOeSBI
must
be changed
by
the calling
program.
IoeSBE
must contain the
address
of
the
last
byte
of
a
sector
bu~f-eT'.
The
sector
buffeT'
must
be
an
integral
number
of
sectors
in
size
(see
sec t ion
25.3.
1.
20).
The
buffer
described
by
IOCSBS
and
IOCSBE
indicates· the
maximum
number
of
sectors
that
can
be
processed
starting
with
the
logical
sector
whose number is in IDCLSN,
A is indeterminate.
B
=
Th
e
contents
oT
th e IOCSTA entry.
If
no erT'ors occurred, B
will
be
zero.
A
non-~ero
value
indicates that an
error occurred.
X is
unchanged.
Page
25-52
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