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Sharp MZ-800 Service Manual page 14

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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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