I
MZ-800
4-2-5. Scroll
1)
Scrolling is possible
for
both
horizontal
and
vertical
directions
by
means
of
software
offset.
The
following
four
registers are
use~
for
scroll
control.
a.
Scroll start address register: SSA (7-bit)
b.
Scroll end address register: SEA (7-bit)
c.
Scroll
width
register:
SW
= SEA-SSA (7-bit)
d. Scroll offset register:
SOF (10-bit)
(
x y z
I
SEA
+--
__
I
I
I
I
!
l,
___
_
)
---
2)
Control
of
scroll starts
by
the
initialization
of
the
scroll control register.
SSA
= $0
SEA = $7D
SW
= $7D
SOF = $0
3)
Way
of
smooth
scrolling
SOF = $0
~
$5
Programming
"SOF =
$5"
makes
the
display
screen
shifted one line up.
The highest line (address:
$0 - $27) is then assigned
to
the
lowest
line
($1
F18
-.:
$1
F3F).
As
normal
scroll
involves
updating
of
the data
for
the
lowest
line,
the
data
of
address
$1
F18
-
$1
F3F
are
updated.
SOF = $5
~
$0
By reducing the value
of
SOF
by
"5",
it
makes the
screen shifted one line
down.
SEAL-
____________________________
~
13
4)
Line scroll
SOF =
$O~
$28
Programming
"SOF =
$28"
makes
the
display screen
shifted
eight
lines up. Data on the highest line
therefore shifted
to
the
bottom
line.
Programming
"$28
~
$0"
makes the
display
screen
shifted
eight
lines
down,
and
the
line
on
the
bottom
moves
to
the
highest
line.
5)
Screen
split
Appropriate
deviation
of
SSA. SEA, and
SW
permits
to
divide
the
screen
into
three sections
of
®,
® and
©.
Though
the
section ® is
permitted
to
scroll, sections
® and © are
not
permitted
to
scroll.
See the
figure
to
explain
with.
@
SSA-.
®
SEA-.
©
Assume
now
that
the
top
of
the
section ® is on the
5th line
(40 raster) and
the
top
of
the section © is on
the 18th line (144 raster).
Attention
must
be paid to
the fact
that
values SSA and SEA are used
for
assigning lines. Scroll registers are set
with
the
following
values.
SSA
= $19
SEA
=
$5A
SW
=
$41
SOF = $0
In
this
occasion,
it
needs
to
initialize
the
screen that
has been displayed.
"SOF =
$5"
must
be program-
med
to
scroll ® one line. Then,
only
the
section ® is
shifted
up, and
the
highest
line
of
® moves
to
the
bottom
line
of
®.
Programming
"SOF =
$A"
makes
it
scrolled one
more
line.
SOF
~
SW
Scroll offset (SOF)
should
necessarily be
within
a
range
of
the
scroll
width.
Display is
not
assured
with
SOF set greater than SW.
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