Datasheet

223
ATmega329/3290/649/6490
2552I–AVR–04/07
segments on the LCD display must therefore be able to be fully charged/discharged
within 2 or 2.7ms, depending on the number of common pins.
Minimizing power
consumption
By keeping the percentage of the time the LCD drivers are turned on at a minimum, the
power consumption of the LCD driver can be minimized. This can be achieved by using
the lowest acceptable frame rate, and using low power waveform if possible. The drive
time should be kept at the lowest setting that achieves satisfactory contrast for a partic-
ular display, while allowing some headroom for production variations between individual
LCD drivers and displays. Note that some of the highest LCD voltage settings may
result in high power consumption when V
CC
is below 2.0V. The recommended maximum
LCD voltage is 2*(V
CC
- 0.2V).
Mode of Operation
Static Duty and Bias If all segments on a LCD have one electrode common, then each segment must have a
unique terminal.
This kind of display is driven with the waveform shown in Figure 99. SEG0 - COM0 is
the voltage across a segment that is on, and SEG1 - COM0 is the voltage across a seg-
ment that is off.
Figure 99. Driving a LCD with One Common Terminal
1/2 Duty and 1/2 Bias For LCD with two common terminals (1/2 duty) a more complex waveform must be used
to individually control segments. Although 1/3 bias can be selected 1/2 bias is most
common for these displays. Waveform is shown in Figure 100. SEG0 - COM0 is the volt-
age across a segment that is on, and SEG0 - COM1 is the voltage across a segment
that is off.
V
LCD
GND
V
LCD
GND
V
LCD
GND
-V
LCD
SEG0
COM0
SEG0 - COM0
Frame Frame
V
LCD
GND
V
LCD
GND
GND
SEG1
COM0
SEG1 - COM0
Frame Frame