Apple IIe - Page 253

The
System
Monitor
253
to
display.
The
user can
quickly
step
through
memory
eight
bytes
at a
time
by
merely
pressing
the
[return]
key.
The
mon
i
tor
will
display
eight
bytes
in
a
row
,
but
it
is
particular
which
eight
it
displays.
The
monitor
will
display
an address
ending
with
a
zero
or
an
eight
followed
by
the
contents
of
that
address
as
well
as
the
data
of
the
next
eight
bytes.
Therefore
,
the
first
time
[
return]
is
pressed,
the
balance
of
whichever
line
the
monitor
would
have
displayed
will
be
printed.
Each
successive
[return]
produces
the
next
display line.
Monitor
commands
can be
combined
into
one
command
line
.
For
example
,
to
display
the
contents
of
locations
0300
to D31C
Hex,
type:
*D300.D31C
D300-AF
D3
48
20
9A
D3
68
20
D308-2E
DO
AE
23
03
60
20
F9
D310-D2
4C
7D
DO
AD
25
03
4A
D318-20
90
D3
20
75
Register
Examine
When
the
monitor
is
activated,
the
contents
of
the
registers
in
the
6502
are saved
in
page-zero. The
only
register
not
saved
is
the
program
counter
.
The
accumulator
,
X-register, Y-
reg
ister,
pro
-
cess
status register
and
stack
pointer
are saved
in
memory
lo
ca-
tions
45
through
49, respectively. Instead
of
typing
45.49
to
dis-
play
the
contents
of
these registers,
the
monitor
provides
the
register
examine
, CTRL-E,
command.
After
displaying
the
con
-
tents
of
these registers,
the
monitor
stores
45
,
the
address
of
the
accumulator
,
as
the
opened
addre
ss.
*CTRL-E
A=18
X=FE
Y=FF
P=BO
S=F8
Changing Memory
We
have
now
seen
how
any
locat
i
on
in
memory
ca
n
be
di
s-
played.
If
Picasso
could
only
have
looked
at his canv
as
withou
t
changing
it
,
how
much
of
an a
rt
i
st
would
he have been? The
same
concept
applies
to
th
e
programmer
a
nd
his canvas, the
computer
.