Radio Shack TRS-80 model III Owner's Manual page 109

TRS-80
MODEL
III
DISK
SYSTEM
DEFUSR
Define Point of Entry
for
USR
Routine
n
equals one
of
the
digits 0,
1 ,.,.,9;
if
n
is
omitted,
is
assumed.
defusr
lets
you
define the entry points
for
up
to 10
machine-language
routines.
In
non-Disk
basic,
the addresses were POKEd
into
ram.
This
poke method
cannot be used
in
Disk
basic.
Examples
DEFUSR3
=
&H7DBB
assigns the entry point
X'7D00\
32000
decimal,
to the
USR3
call.
When
your
program
calls
USR3,
control
will
branch
to
your
subroutine beginning
at
x'7D00\
DEFUSR
=
(BASE
+ IS)
assigns
start
address (base
+
16)
to the usro
routine.
Note:
When
decimal
addresses
are
given, they
are
evaluated
as
signed two-byte
integers. So, for addresses above
32767,
use desired decimal address -65536.
See
usR/i.
INSTR
Search
for Specified String
position specifies the position
in string 1
where
the search
is to begin.
position
is
optional;
if it is
not supplied, search automatically begins
at the
first
character
in string
1.
(Position
1 is
the
first
character
in
108