Datasheet

Chapter 9 Liquid Crystal Display Driver (S08LCDV1)
MC9S08LC60 Series Data Sheet: Technical Data, Rev. 4
166 Freescale Semiconductor
9.6.1.2 Segment On Driving Waveform
The voltage waveform across the “f” segment of the LCD (between BP1 and FP0) is illustrated in
Figure 9-21. As shown in the waveform, the voltage level reaches the value V
3
therefore the segment will
be on.
Figure 9-21. “f” Segment Voltage Waveform
9.6.1.3 Segment Off Driving Waveform
The voltage waveform across the “e” segment of the LCD (between BP2 and FP0) is illustrated in
Figure 9-22. As shown in the waveform, the voltage does not reach the voltage V
3
threshold therefore the
segment will be off.
Figure 9-22. “e” Segment Voltage Waveform
9.6.2 LCD Contrast Control
Contrast control for the LCD module is achieved when LCD power supply is adjusted above and below
the LCD threshold voltage. The LCD threshold voltage is the nominal voltage required to energize the
LCD segments. For 3-V LCD glass, the LCD threshold voltage is 3-V; while, for 5-V LCD glass, the LCD
threshold voltage is 5-V. By increasing the value of the LCD threshold voltage, the energized segments on
the LCD glass will become more opaque. Decreasing the value of the LCD threshold voltage makes the
energized segments on the LCD glass become more transparent. The LCD power supply can be adjusted
to facilitate contrast control by using external components like a variable resistor. Figure 9-23 shows two
circuits that could be used to implement contract control.
BP1–FP0
+V
3
+V
2
+V
1
–V
1
–V
2
–V
3
V
0
+V
2
+V
1
–V
1
–V
2
–V
3
+V
3
V
0
BP2–FP0