Apple IIe - Page 267

The
System
Monitor
267
grammer
can
conveniently
list a
program
which
would
fill
more
than
one
screen.
Executing a
Machine
Language Program
The
monitor's
GO
command
is
used
to
execute
a
machine
lan-
guage
program.
When
GO
is
executed,
the
microprocessor's registers
will
be
loaded
with
the
values stored
in
addresses
$45
to
$49
as
follows
:
•
The
microprocessor's
accumulator
will
be
loaded
with
the
value stored
in
address
$45.
• The X register
will
be
loaded
with
the
value
stored
in
$46.
• The
Y register
will
be
loaded
with
the
value stored
in
$47.
•
The
processor status register
will
be
loaded
with
the
value
stored
in
$48.
• The stack
pointer
will
be
loaded
with
the
value
stored
in
$49.
Once
the
registers have
been
loaded,
a
JSR
(Jump
to
Subroutine)
command
will
be
executed
to
the
last
opened
memory
location
.
Since
the
monitor
treats all programs
as
subroutines,
a
RTS
(Return
from
Subroutine)
instruction
should
be
the
last
instruc-
tion
in
the
program.
We
will
illustrate
the
usage
of
GO
using
the
following
example
(which
you
probably
have already
entered)
.
!300:
JSR
FBDD
! JMP
300
This
program
can
be
executed
by
entering
the
following:
*300
G