Radio Shack TRS-80 model III Owner's Manual page 84

TRSDOS
the
file
for use.
If
the
name
is
not found,
a
new
file is
created
with
the filespec
name.
Entry Conditions
(HL)
=
buffer
(see
beginning of
this
section for notation)
(DE)
=
DCB
B
=
LRL
CALL
$INIT
Exit Conditions
iy
—
changed
z
=
OK
c
carry
flag
is
on
if
a
new
file
was
created
a
=
trsdos
error code. (Error
codes
listed at
end
of
this
chapter)
$OPEN—
17444/X'4424'
$open
provides
a
way
to
open
the
dcb
of
a
file
which
already
exists in the
directory.
The dcb
must contain
the filespec
of
the
file to
be
opened
before entry
to
$open.
Entry Conditions
(HL)
=
BUFFER
(DE)
=
DCB
B
=
LRL
CALL $OPEN
Exit Conditions
Z
=
OK
z
=
if file
does
not
exist.
a
=
trsdos
error code.
iy
=
changed
$POSN—
17474/X'4442'
$posn
positions a
file to
read or write a
randomly
selected logical record.
Since
it
deals
with
logical records, the
proper computation
is
done
to
locate
which
physical record(s) contain the
data.
Following
a
$posn
with a
$read
or
$write
will transfer
the record to/from
ram.
79