Renesas F-ZTAT H8 Series, Hardware Manual

Page: 400 / 562

13. Dot Matrix LCD Controller (H8/3857 Group)
Rev.3.00 Jul. 19, 2007 page 374 of 532
REJ09B0397-0300
Table 13.8 Contrast Control Ranges
Bias LCD Drive Voltage: V
DR
Contrast Control Range
1/5 bias
drive
5
×
R
5
×
R + V
R
×
(V
LCD
– V
SS
)
1/4 bias
drive
4
×
R
4
×
R + V
R
×
(V
LCD
– V
SS
)
R
5
×
R + V
R
×
(V
LCD
– V
SS
)
≥
0.4 [V]
V
R
5
×
R + V
R
×
(V
LCD
– V
SS
)
≥
0.4 [V]
R
4
×
R + V
R
×
(V
LCD
– V
SS
)
≥
0.4 [V]
V
R
4
×
R + V
R
×
(V
LCD
– V
SS
)
≥
0.4 [V]
• LCD drive voltage
adjustment range:
• V5
−
V
SS
potential
difference limit:
• V
LCD
−
V1 potential
difference limit:
• LCD drive voltage
adjustment range:
• V5
−
V
SS
potential
difference limit:
• V
LCD
−
V1 potential
difference limit:
0.758
×
(V
LCD
– V
SS
)
≤
V
DR
≤
0.980
×
(V
LCD
– V
SS
)
0.714
×
(V
LCD
– V
SS
)
≤
V
DR
≤
0.976
×
(V
LCD
– V
SS
)
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
SS
) can be kept low. If the LCD drive
voltage is inadequate even with a low V
ci
voltage and use of the 3X step-up circuit, or if the output
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 =
1
N + 1
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.