Datasheet

Liquid Crystal Display (LCD) Driver
Functional Description
MC68HC908LJ24/LK24 — Rev. 2.1 Data Sheet
Freescale Semiconductor Liquid Crystal Display (LCD) Driver 355
17.5.1 LCD Duty
The setting of the LCD output waveform duty is dependent on the
number of backplane drivers required. Three LCD duties are available:
• Static duty — BP0 is used only
• 1/3 duty — BP0, BP1, and BP3 are used
• 1/4 duty — BP0, BP1, BP2, and BP3 are used
When the LCD driver module is enabled the backplane waveforms for
the selected duty are driven out of the backplane pins. The backplane
waveforms are periodic and are shown are shown in Figure 17-5,
Figure 17-6, and Figure 17-7.
17.5.2 LCD Voltages (V
LCD,
V
LCD1,
V
LCD2
, V
LCD3
)
The voltage V
LCD
is from the V
LCD
pin and must not exceed V
DD
. V
LCD1
,
V
LCD2
, and V
LCD3
are internal bias voltages for the LCD driver
waveforms. They are derived from V
LCD
using a resistor ladder (see
Figure 17-3).
The relative potential of the LCD voltages are:
•V
LCD
= V
DD
•V
LCD1
= 2/3 × (V
LCD
– V
bias
)
•V
LCD2
= 1/3 × (V
LCD
– V
bias
)
•V
LCD3
= V
bias
The V
LCD3
bias voltage, V
bias
, is controlled by the LCD contrast control
bits, LCCON[2:0].
17.5.3 LCD Cycle Frame
The LCD driver module uses the CGMXCLK (see Section 7. Oscillator
(OSC))as the input reference clock. This clock is divided to produce the
LCD waveform base clock, LCDCLK, by configuring the LCLK[2:0] bits
in the LCD clock register. The LCDCLK clocks the backplane and the
frontplane output waveforms.