HD66740 Datasheet, PDF (44/95 Pages) Hitachi Semiconductor – 112 x 80-dot Graphics LCD Controller/Driver

HD66740
n-raster-row Reversed AC Drive
The HD66740 supports not only the LCD reversed AC drive in a one-frame unit (B-pattern waveform)
but also the n-raster-row reversed AC drive which alternates in an n-raster-row unit from one to 32
raster-rows (C-pattern waveform). When a problem affecting display quality occurs, such as crosstalk
at high-duty driving of more than five lines (1/40 duty), the n-raster-row reversed AC drive (C-pattern
waveform) can improve the quality. Determine the number of raster-rows n (NW bit set value + 1) for
alternating after confirmation of the display quality with the actual LCD panel. However, if the number
of AC raster-rows is reduced, the LCD alternating frequency becomes high. Because of this, the charge
or discharge current is increased in the LCD cells.
1 frame
1 frame
1 2 3 4 5 6 7 8 9 10 11 12 13 79 80 1 2 3 4 5 6 7 8 9 10 11 12 13 79 80 1 2 3
B-pattern
waveform drive
• 1/80 duty
C-pattern
waveform drive
• 1/80 duty
• 11-raster-row
reversal
• Without EORs
C-pattern
waveform drive
• 1/80 duty
• 11-raster-row
reversal
• With EORs
Note: Specify the number of AC drive raster-rows and the necessity of EOR so that the DC bias is not generated for
the liquid crystal.
Figure 21 Example of an AC Signal under n-raster-row Reversed AC Drive
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