Radio Shack TRS-80 Trsdos & Disk Basic Reference Manual page 77

TRSDOS
Technical Information
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
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
)
DE=
> xxxx
Registers
DE
contain the address of (point
to)
xxxx
in
machine
format.
(If
address
of
xxxx=5AF1H
then the values
in
the
registers are:
D=5A;E=F1)
B=
xx
Register
B
contains the
numeric
value of
xx
in
binary form.
If
xx=64
decimal,
then
B=40H.
A=
xx
Register
A
contains the
numeric
value
of
xx
in
binary form.
If
.0;= 127 decimal, then
A=7FH.
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.
Z=OK
Zero
flag
is
set
(OK)
if
successful return
from
the
system
routines.
X'nnnn' Hard
RAM
address
in
nex
notation
(e.g.,
402D
is
X'402D').
LRL
Logical
Record
Lengtn. 1-255 bytes only.
You
can define records
any length
you
wish
up
to
255
bytes
maximum.
A
length of zero
is
a special
case for physical records only,
and
indicates
the
LRL=256
bytes.
BUFFER
256
user designated bytes
in
RAM
for
TRSDOS
to
read
sectors
from
or write sectors
into. If
LRL=0,
this
area
is
the responsibility
of the user
to
manage
before
and
after I/O.
TRSDOS
manages
this
area
if
LRL
is
between
1
and 255
bytes.
Do
not
alter this
area
when
using
logical
record
processing.
UREC
User record: the address
of the contiguous
RAM
byte-string assigned
by
the user as his
logical
record
area. Its
length
must
be equal
to
LRL.
It is
a
different area
from
BUFFER.
6-5