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INPUT/OUTPUT FUNCTIONS
25.3 -- Device Independent I/O Functions
7
IO
The
format
or
the IOCDTT byte is shown below:
6
5
4
3
2
; 5
i
a
i T
l F
;
1
o
M
Mode
flag
Non-file
Tormat
rlag
Truncate
~lag
Open/closed flag
Sector/record flag
1/0
transrer Tlag
Regardless of the
t~pe
of
device
being
accessedl
the
non-file
format
flag
(F)
and
the mode flag
(M) are to be
initialized by the user.
If the device is
a
diskette
drive,
the
user
may
also change the sector/record flag (5) or the
truncate flag
(T)
between
IIO
function calls.
If
the
flags
are to be changed after the
IOCDTT
byte has been initializedl
care must be taken so that none
of
the system supplied
flags
are
destroyed.
Flags must be itor-ed
II
into the
IOCDTT
to be
set
I
and
/I
and-ed" out of th e IDCDTT to be cleared,
one
e
th e
IOCB has ,been reserved.
The
properties
controlled
by
the various bits of the
IOCDTT are explained below.
10 (Bits 6-7) -- I/O transfer flag
These two bits
are
controlled exclusively by the
I/O
functions themselves.
They should not be set or
changed by the user in any case.
If
'bit
6
is set
to
one,
the device driver T'ecognizes
an
output tl"ansfer.
IT bit 7
is set
to one,
the device driver
recognizes
an
input
transfer.
The
device driver will not be
able to input or
output
a character iT both
of
these
bits are zero or one.
---...
Page
25-20
I
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