HD66750 Datasheet, PDF (61/96 Pages) Hitachi Semiconductor – 128 x 128-dot Graphics LCD Controller/Driver with Four-grayscale Functions

HD66750/1
Liquid-crystal-display Drive-bias Selector
An optimum liquid-crystal-display bias value can be selected using the BS2-0 bits, according to the liquid
crystal drive duty ratio setting (NL3-0 bits). The liquid-crystal-display drive duty ratio and bias value can
be displayed while switching software applications to match the LCD panel display status. The optimum
bias value calculated using the following expression is a logical optimum value. Driving by using a lower
value than the optimum bias value provides lower logical contrast and lower liquid-crystal-display voltage
(the potential difference between V1 and GND), which results in better image quality. When the liquid-
crystal-display voltage is insufficient even if a seven-times booster is used, when the boosting driving
ability is lowered by setting a high factor for the booster, or when the output voltage is lowered because the
battery life has been reached, the display can be made easier to see by lowering the liquid-crystal-display
bias.
The liquid crystal display can be adjusted by using the contrast adjustment register (CT5-0 bits) and
selecting the booster output level (BT1/0 bits).
Table 21
1
Optimum bias value for 1/N duty ratio drive voltage =
N+1
Optimum Drive Bias Values
LCD drive
duty ratio
(NL3-0 set
value)
Optimum
drive bias
value
(BS2-0 set
value)
1/128
1111
1/11
000
1/120 1/112
1110 1101
1/11 1/11
000 000
1/104 1/96
1100 1011
1/11 1/10
000 001
1/88
1010
1/10
001
1/80
1001
1/10
001
1/72
1000
1/9
010
1/64
0111
1/9
010
1/32
0100
1/6
101
1/24
0011
1/6
101
1/16
0010
1/5
100
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