
Liquid Crystal Display Driver (S08LCDV1)
MC9S08LL64 MCU Series Reference Manual, Rev. 5
240
Freescale Semiconductor
backplane. The LCDWF registers can then activate (display) the corresponding LCD segments on an LCD
panel.
The LCDWF registers control the on/off state for the segments controlled by the LCD pins defined as front
planes and the active phase for the backplanes. Blank display modes do not use the data from the LCDWF
registers. When using the LCDWF register for frontplane operation, writing a 0 turns the segment off.
For pins enabled as backplane, the phase of the backplane (A-H) is assigned by the LCDWF register for
the corresponding backplane pin. For a detailed description of LCD module operation for a basic
13.4.1
LCD Driver Description
The LCD module driver has 8 modes of operation:
1/1 duty (1 backplane) (Phase A), 1/1 bias (2 voltage levels)
1/2 duty (2 backplanes) (Phase A, B), 1/3 bias (4 voltage levels)
1/3 duty (3 backplanes) (Phase A, B, C), 1/3 bias (4 voltage levels)
1/4 duty (4 backplanes) (Phase A, B, C, D), 1/3 bias (4 voltage levels)
1/5 duty (5 backplanes) (Phase A, B, C, D, E), 1/3 bias (4 voltage levels)
1/6 duty (6 backplanes) (Phase A, B, C, D, E, F), 1/3 bias (4 voltage levels)
1/7 duty (7 backplanes) (Phase A, B, C, D, E, F, G), 1/3 bias (4 voltage levels)
1/8 duty (8 backplanes) (Phase A, B, C, D, E, F, G, H), 1/3 bias (4 voltage levels)
All modes are 1/3 bias. These modes of operation are described in more detail in the following sections.
13.4.1.1
LCD Duty Cycle
The denominator of the duty cycle indicates the number of LCD panel segments capable of being driven
by each individual frontplane output driver. Depending on the duty cycle, the LCD waveform drive can be
categorized as static or multiplexed.
In static-driving method, the LCD is driven with two square waveforms. The static-driving method is the
most basic method to drive an LCD panel, but because each frontplane driver can drive only one LCD
segment, static driving limits the LCD segments that can be driven with a given number of frontplane pins.
In static mode, only one backplane is required.
In multiplexed mode, the LCD waveforms are multi-level and depend on the bias mode. Multiplex mode,
depending on the number of backplanes, can drive multiple LCD segments with a single frontplane driver.
This reduces the number of driver circuits and connections to LCD segments. For multiplex mode
operation, at least two backplane drivers are needed. The LCD module is optimized for multiplex mode.
The duty cycle indicates the amount of time the LCD panel segment is energized during each LCD module
frame cycle. The denominator of the duty cycle indicates the number of backplanes that are being used to
drive an LCD panel.
The duty cycle is used by the backplane phase generator to set the phase outputs. The phase outputs A-H
are driven according to the sequence shown below. The sequence is repeated at the LCD frame frequency.