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14.6 Explanation of Operation of LCD Controller/Driver
The LCD controller/driver performs control and driving for LCD display.
„
Explanation of LCD controller/driver operation
The following setting is needed for LCD display:
bit 7
RESV1 RESV0 VSEL
LCRL
0
bit 15
––
LCRH
Display RAM
1960
to 196B
H
H
When the above setting is made and the selected clock for frame cycle generation is oscillating, the LCD
panel driving wave form are output to the common/segment output pins (COM0 to COM3, SEG0 to SEG16)
in accordance with the display RAM data.
The clock for frame cycle generation can be switched even during LCD display. However, in this case, there
is a possibility of flicker at switching, so stop temporarily by blanking (LCRL: BK = 1), and then switch the
clock.
The display driving output is 2-frame AC waveform selected according to the bias/duty settings.
For 1/2 duty, output of the COM2/COM3 pin becomes nonselective output waveform. Similarly, for 1/3 duty,
output of the COM3 pin becomes nonselective output waveform.
When the LCD display is stopped (LCRL: MS1, MS0 = 00B) or during reset, both common output pins and
segment output pins are set to the L level.
Note:
When the selected clock for frame cycle generation stops during LCD display, the AC generator
circuit stops, passing the current directly through the liquid crystal element. Consequently, the LCD
display must be stopped before the clock stops. The condition for stopping the original oscillation
clock depends on the standby mode selection.
„
LCD driving waves
When the LCD is driven by direct current, chemical changes occur in the liquid crystal causing degradation.
So, the LCD controller/driver has an AC generator and drives the LCD by means of 2-frame AC waveform.
There are three types of output waveform as shown below:
• Based on 1/2 bias and 1/2 duty
• Based on 1/3 bias and 1/3 duty
• Based on 1/3 bias and 1/4 duty
LCD CONTROLLER/DRIVER
bit 6
bit 5
bit 4
BK
0
0
bit 14
bit 13
bit 12
SEG5 SEG4
––
Display data
Fig. 14.12 Setting of LCD Controller/Driver
bit 3
bit 2
bit 1
MS1
MS0
FP1
Other than 00
bit 11
bit 10
bit 9
SEG3 SEG2 SEG1 SEG0
14-19
bit 0
FP0
bit 8
: Indicates bit used
0
: 0 set
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