Radio Shack TRS-80 Owner's Manual page 91

as M
mmmmmmmmmm
EsBSS
Y^SMfZMMiM^MIMMsMMM^
*c
granules
after
the
one containing
the
file's
eof
mark,
are
recovered
and
returned
to
the
system
when
the
file is
closed.
A TRSDOS
file
FILE;
LRN1
LRN2 LRN3
EXTENT
1
LRNN EOF
EXTENT
2
SEGMENT:
GRANULE
1
GRANULE
2
GRANULE
32
GRANULE:
SECTOR
X
SECTOR X +
SECTOR
X +
2
BYTE1 BYTE
2
BYTE
3
BYTE
256
SECTOR:
LRN:
Logical
Record
Number,
used
to
specify
an
individual,
user-defined
logical record.
Such
a logical
record
is
the smallest unit of
information
which
can be addressed during disk input/output
(a
physical record
is
the unit
which
is
actually
read
from
or written
to
disk).
File:
A
group of logical records; the largest unit
of information
which
can
be addressed by
a
trsdos command.
Sector:
A
physical record,
composed
of
256
contiguous bytes.
Granule:
The
minimum
allocatable unit
of storage for
any
file.
Extent:
One
contiguous
allocation
of granules.
System
Routines
for
Assembly-Language I/O
This information
is
provided
for
customers
who
wish
to
write
their
own
assembly level
i/o
routines.
An
explanation of
the calling
sequence and
parameters
for
each
necessary
i/o
routine
is
given.
A
knowledge of
z~80
machine
code
is
assumed.
The
following
notations are standard
in this section:
(HL)
=
xxxx
-XX
Registers
hl
contain the
address of
(point
to)
xxxx
in
machine
format.
(If
address of xxxx
=
34B2H then the values
in
the
registers
are:
h
=
34;
l
=
B2).
Other
register pairs will also
be
indicated
this
way.
Register
a
contains the
numeric
value of
xx
in
binary form.
Register
a
is
used
to
return the
trsdos
error
code
for
i/o calls.
A
complete
list
of error
codes and
their
meanings
appears
at
the
end of
this
chapter.
Other
registers will
also
be
indicated
this
way.
75