RA8835A
Version 1.0
Dot Matrix LCD Controller
8-4 Smooth Horizontal Scrolling
Figure 8-7 illustrates smooth display scrolling to the left. When scrolling left, the screen is effectively
moving to the right, over the larger virtual screen. Instead of changing the display start address SAD
and shifting the display by eight pixels, smooth scrolling is achieved by repeatedly changing the pixel-
shift parameter of the HDOT SCR command. When the display has been scrolled seven pixels, the
HDOT SCR pixel-shift parameter is reset to zero and SAD incremented by one. Repeating this
operation at a suitable rate gives the appearance of smooth scrolling.
To scroll the display to the right, the reverse procedure is followed. When the edge of the virtual screen
is reached, the microprocessor must take appropriate steps so that the display is not corrupted. The
scroll must be stopped or the display modified.
Note that the HDOT SCR command cannot be used to scroll individual layers.
HDOT SCR
parameter
SAD
SAD+1
SAD+2
P1=00H
Magnified
AP
P1=01H
SAD=SAD
Display
C/R
P1=02H
P1=03H
Virtual screen
P1=07H
P1=00H
SAD=SAD+1
Not visible
Visible
Figure: 8-7 HDOT SCR Example
Note: The response time of LCD panels changes considerably at low temperatures. Smooth scrolling
under these conditions may make the display difficult to read.
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