HD66760 Datasheet, PDF (70/105 Pages) Hitachi Semiconductor – 104 X 80-dot Graphics LCD Controller/Driver for 256 Colors

HD66760
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 six-times step-up circuit is used, when the step-up driving ability is
lowered by setting a high factor for the step-up circuit, 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 (CT6–0 bits) and selecting
the step-up output level (BT1/0 bits).
Optimum bias value for 1/N duty ratio drive voltage = ¹
N+1
Table 36 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
001
1/72
1000
1/9
010
1/64
0111
1/9
010
1/56
0110
1/8
011
1/48
0101
1/8
011
1/40
0100
1/7
100
1/32
0011
1/6
101
1/24
0010
1/6
101
1/16
0001
1/5
110