
360
CHAPTER 14 LCD CONTROLLER/DRIVER
14.4 Operation of LCD Controller/Driver
The LCD controller/driver provides the necessary control and drive for an LCD display.
s Operation of LCD Controller/Driver
Figure 14.4-1 "LCD Controller/Driver Settings" shows the settings required to operate the LCD
display.
Figure 14.4-1 LCD Controller/Driver Settings
Once the above settings have been made, if the selected clock for frame cycle generation is
running, LCD panel driving waveforms reflecting the contents of display RAM will be output at
the segment and common output pins (COM0 to COM3 and SEG0 to SEG13).
Although the clock for frame period generation can be switched even while the LCD is
displaying data, the display may flicker when the switching occurs. This can be avoided by
temporarily blanking the display (LCR1: BK = 1), etc. while switching.
The display driving output is a two-frame a.c. waveform for which the bias level and display duty
cycle is selected by settings.
When the P70/COM2 and P71/COM3 pins are set as COM outputs, deselection levels are
output in the waveforms at the COM2 and COM3 outputs in 1/2 duty ratio operation, and at the
COM3 output in 1/3 duty ratio operation.
When LCD display operation is stopped (LCR1: MS1 = MS0 = 00B), and during reset, all COM
and SEG output pins are taken "L".
Check:
If the selected frame cycle generate clock were to stop while the LCD display is operating,
the circuit that converts the waveform from d.c. to a.c. would also stop, causing a d.c.
voltage to be applied to the liquid crystal cells.
The LCD display must be therefore be
stopped before the clock is stopped. The conditions under which the main clock (timebase
timer) and subclock are stopped are a function of the clock mode and standby mode. Also
note that when the timebase timer is selected as the frame clock source (LCR1: CSS = 0),
clearing the timebase timer will affect the frame cycle.
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
LCR1
CSS
LCEN
VSEL
BK
MS1
MS0
FP1
FP0
0
Display RAM
060H to 06BH
Display data
: Used bit
1 : Set "1".
0 : Set "0".
Other than "00H"