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INPUT/OUTPUT FUNCTIONS
25.3 -- Device Independent I/O Functions
must
not
contain information
ror
an
open file
{L
e.
~
the first file
must
have
been
properltj
closed>.
The
.OPEN
function
does
not
Torce
an
already-open file to be closed.
IOCDTT
must
have
the
"M"
bits set for
inputi
output;
0'1'
update
modes~
The
update
modes
are
only
valid
for
diskette devices.
In
addition,
the
"F" bit must
~pecify
file or non-file
format.
The non-file format mode
is
invalid
for
diskette
devices.
The
US"
bit must indicate the
subsequent
access method to be used.
Sector IIO
is invalid Tor
non-diskette devices.
lOCDBS
must
contain
a
buffer
start
address
unless
diskette IIO (either
record
or
logical
sector)
or
the
non-file
format
mode
has
been
speciried in the
IOCDTT.
The
data
buffer described
by
IOCDBS and IOCDBE
is
used
- for
FDR
proc es sing
wi th
non-diskette
devices.
If
used,
it
must be large enough
to
accommodate
an
FDR
(s e c
t
i
on
24. 3. 4).
IOCDBE
must contain
a
buffer end address
unless diskette 1/0 (either record or
logical
sector)
or
the
non-file
format mode has been specified in the
IOCDTT.
The data buffer described
by
IOCDBS and IOCDBE
is
used
for
FDR
processing with non-diskette devices.
If used,
it must be large
enough
to
accommQdate an FDR (section 24.3.4>.
IOCNAM
must
contain
a
valid
MDOS-formatted file name
unless
the
non-file
format
mode
has
been
specified in the IOCDTT or unless the
first
b~te
of
file
name is binary
zero.
In the file format mode
on
a
non-diskette
device being opened for.
input,
the .
OPEN
function will
cause
a
search
to
be
performed
for the
first
FDR
iT the first byte of IOCNAM
is
a
binary
zero.
This file
will
then be used by the subsequent record
input
requests.
Otherwise,
the file
name supplied
in
IOCLUN,
IOCNAM,
and
IOCSUF
is
searched
for
or created
(depending on M of IOCDTT).
Page
25-35
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