62
USR
(user)
Calls out and executes in BASIC the machine language program.
Format:
USR
«address>
,
<input
character variable> ,
<output
character variable)
<address>
: numerical data
or
4-digit hexadecimal number
Abbreviated form:
U.
Explanation:
• Calls out and executes the machine language program during BASIC program
execution. This
is
the same
as
the branch command and CALL
<address>
to the
machine language subroutine. Consequently, when there
is
a return command in a
machine language program, control moves to the next statement following the
executed statement.
• At the point
in
time when the machine language program
is
called out, the value
following the
<input
character variable>
is
set in the register.
DE
register: heading address
of
memory area
of
<input
character variable>
B register: length
of
<input
character variable>
IX register: address if error-processing routine
is
announced
•
At
the point
in
time
of
return from the machine language program, the value
of
the
data indicated
by
the subsequent register becomes the
<output
character
variable>.
DE
register: heading address
of
memory area
of
<output
character variable>
B register: length
of
<output
character variable>
•
If
error-processing
is
necessary in a machine language program, the following
process occurs.
(1)
An
error-processing routine
is
established by the ON
ERROR
GOTO
statement in the BASIC program.
(2) An error code
is
substituted
in
the A register, and
is
jumped to the address
indicated
by
the IX register.
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