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13. Dot Matrix LCD Controller (H8/3857 Group)
Table 13.8 Contrast Control Ranges
Bias
LCD Drive Voltage: V
5 × R
1/5 bias
× (V
drive
5 × R + V
R
4 × R
1/4 bias
× (V
4 × R + V
drive
R
13.3.15 LCD Drive Bias Selection Circuit
The ideal bias value that gives the best contrast is calculated using the equation shown below. If
drive is performed at a bias value lower than the optimum, contrast will deteriorate, but the LCD
drive voltage (the potential difference between V1 and V
voltage is inadequate even with a low V
voltage falls and the LCD display becomes faint as batteries wear out, for instance, the display can
be made clearer by decreasing the LCD drive bias.
Optimum bias value for 1/N duty drive =
Notes: 1. When using 1/5 bias, leave the V3 and V4 pins open.
2. When using 1/4 bias, short the V3 and V4 pins.
3. The V3 and V34 pins must always be shorted.
Rev.3.00 Jul. 19, 2007 page 374 of 532
REJ09B0397-0300
Contrast Control Range
DR
• LCD drive voltage
adjustment range:
• V5−V
potential
SS
– V
)
LCD
SS
difference limit:
−V1 potential
• V
LCD
difference limit:
• LCD drive voltage
adjustment range:
• V5−V
potential
– V
)
SS
LCD
SS
difference limit:
−V1 potential
• V
LCD
difference limit:
voltage and use of the 3X step-up circuit, or if the output
ci
0.758 × (V
– V
LCD
R
× (V
LCD
5 × R + V
R
V
R
× (V
LCD
5 × R + V
R
0.714 × (V
– V
LCD
R
× (V
LCD
4 × R + V
R
V
R
× (V
LCD
4 × R + V
R
) can be kept low. If the LCD drive
SS
1
N + 1
) ≤ V
≤ 0.980 × (V
SS
DR
LCD
) ≥ 0.4 [V]
– V
SS
) ≥ 0.4 [V]
– V
SS
) ≤ V
≤ 0.976 × (V
SS
DR
LCD
) ≥ 0.4 [V]
– V
SS
) ≥ 0.4 [V]
– V
SS
– V
)
SS
– V
)
SS
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