Radio Shack TRS-80 Owner's Manual page 131

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Examples
NAME
Renumbers
the entire
program:
10,
20, 30,
. . .
NAME 6000*50130 .100
Renumbers
all
lines
numbered from 5000
up; the
first
renumbered
line will
become 6000, and
the
following
lines will
be incremented by
100. All
line
references within
your
program
will
be
renumbered
also.
USRn
Call
to
User's
External Subroutine
r
pj*
usr.i
(nmexp)
where n
specifies
one
of
ten available
\isn
caiis.
/?
=
0.1,2.
.
.9. If
/fls
omitted, zero
is
assumed.
nmexp
is
an integer
from
-
32788
to
32767
artri is
passed
3S an iriegsr
argument
to
the routine.
These
functions
(usro through USR9)
transfer
control to
machine-language
routines
previously defined with
defusr«
statements.
When
a
urs
call is
encountered
in
a statement, control
goes
to the
address
specified
in the
defusrm
statement.
This address
specifies
the entry point to
your
machine-language routine.
Note:
If
you
call
a
usrm routine before defining the routine entry point
with
defusr/i,
an
illegal function
call
error will occur.
You
can pass
one argument and
retrieve
one output value
directly
via the
usr
argument;
or
you can
pass
and
retrieve
arguments
indirectly
via
poke and peek
statements.
Example
1.0
DEFUSR1=&H7D00
20 REM...
MORE PROGRAM LINES HERE
100
A=USRi(X)
The
effect
of
this
sequence
is to:
:
3*giwygBFV~:T:*i
c
- ;!".:-
_;__ -V
-
.:.!
...
'
:
'"
'....:"""
.;...
•....
113