HD66740 Datasheet, PDF (55/95 Pages) Hitachi Semiconductor – 112 x 80-dot Graphics LCD Controller/Driver

HD66740
Liquid Crystal Display Drive Bias Selector
An optimum liquid crystal display bias value can be selected using BS2-0 bits, according to the liquid
crystal drive duty ratio setting (NL3-0 bits). 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 an ideal value where the optimum
contrast is obtained. Driving by using a lower value than the optimum bias value provides lower
contrast and lower liquid crystal display voltage (potential difference between V1 and GND). When the
liquid crystal display voltage is insufficient even if a five-times booster is used or output voltage is
lowered because the battery life has been reached, the display can be made easier to see by lowering the
liquid crystal bias.
The liquid crystal display can be adjusted by using the contrast adjustment register (CT4-0 bits) and
selecting the booster output level (BT1/0 bits).
1
Optimum bias value for 1/N duty ratio drive voltage =
N+1
Table 21
Optimum Drive Bias Values
LCD drive duty ratio
(NL3-0 set value)
Optimum drive bias
value
(BS2-0 set value)
1/80
1001
1/10
1/72
1000
1/9.5
1/64
0111
1/9
1/56
0110
1/8
1/48
0101
1/8
1/40
0100
1/7
1/32
0011
1/6
1/24
0010
1/6
1/16
0001
1/5
1/8
0000
1/4
000 001 010 011 011 100 101 101 110 111
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