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SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
3825 Group
32
Voltage Multiplier (3 Times)
The voltage multiplier performs threefold boosting. This circuit in-
puts a reference voltage for boosting from LCD power input pin
V
L1
. (However, when using a 1/2 bias, connect V
L1
and V
L2
and
apply voltage by external resistor division.)
The voltage multiplier control bit (bit 4 of the LCD mode register)
controls the voltage multiplier.
When voltage is input to the V
L1
pin during operating the voltage
multiplier, voltage that is twice as large as V
L1
occurs at the V
L2
pin, and voltage that is three times as large as V
L1
occurs at the
V
L3
pin.
When using the voltage multiplier; after applying 1.3 V
≤
Voltage
≤
2.3 V
to the V
L1
pin, set the voltage multiplier control bit to “1” to select the
voltage multiplier enable.
When not using the voltage multiplier, apply proper voltage to the
LCD power input pins (V
L1
–V
L3
).
Bias Control and Applied Voltage to LCD
Power Input Pins
To the LCD power input pins (V
L1
–V
L3
), apply the voltage shown
in Table 9 according to the bias value.
Select a bias value by the bias control bit (bit 2 of the LCD mode
register).
Common Pin and Duty Ratio Control
The common pins (COM
0
–COM
3
) to be used are determined by
duty ratio.
Select duty ratio by the duty ratio selection bits (bits 0 and 1 of the
LCD mode register).
Fig. 30 Example of circuit at each bias
Table 9. Bias control and applied voltage to V
L1
–V
L3
Bias value
1/3 bias
1/2 bias
Voltage value
V
L3
=V
LCD
V
L2
=2/3 V
LCD
V
L1
=1/3 V
LCD
V
L3
=V
LCD
V
L2
=V
L1
=1/2 V
LCD
Note :
V
LCD
is the maximum value of supplied voltage for the
LCD panel.
Table 10. Duty ratio control and common pins used
Duty
ratio
2
3
4
Common pins used
Notes 1:
COM
2
and COM
3
are open
2:
COM
3
is open
Bit 1
0
1
1
Bit 0
1
0
1
COM
0
, COM
1
(Note 1)
COM
0
–COM
2
(Note 2)
COM
0
–COM
3
Duty ratio selection bit
V
L3
V
L2
C
2
C
1
V
L1
1/3 bias
when using the voltage multiplier
V
L3
V
L2
C
2
C
1
V
L1
1/3 bias
when not using the voltage multiplier
Open
Open
R2
R1
R3
R1=R2=R3
Contrast control
V
L3
V
L2
C
2
C
1
V
L1
1/2 bias
Open
Open
R4
R5
R4=R5
Contrast control