37
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
3827 Group
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.)
Set each bit of the segment output enable register and the LCD
mode register in the following order for operating the voltage mul-
tiplier.
1. Set the segment output enable bits (bits 0 to 5) of the seg-
ment output enable register to “0” or “1.”
2. Set the duty ratio selection bits (bits 0 and 1), the bias con-
trol bit (bit 2), the LCD circuit divider division ratio selection
bits (bits 5 and 6), and the LCDCK count source selection
bit (bit 7) of the LCD mode register to “0” or “1.”
3. Set the LCD output enable bit (bit 6) of the segment output
enable register to “1.”
4. Set the voltage multiplier control bit (bit 4) of the LCD mode
register to “1.”
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, apply 1.3 V
≤
Voltage
≤
2.3 V to
the V
L1
pin.
When not using the voltage multiplier,apply proper voltage to the
LCD power input pins (V
L1
–V
L3
). Then set the LCD output enable
bit to “1.”
CC
voltage is
applied to the V
L3
pin inside of this microcomputer.
The voltage multiplier control bit (bit 4 of the LCD mode register)
controls the voltage multiplier.
Fig. 40 Example of circuit at each bias
Table 8 Bias control and applied voltage to V
L1
–V
L3
Bias value
1/3 bias
Voltage value
V
L3
=V
LCD
V
L2
=2/3 V
LCD
V
L1
=1/3 V
LCD
Note 1:
V
LCD
is the maximum value of supplied voltage for the
LCD panel.
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 8 according to the bias value.
Select a bias value by the bias control bit (bit 2 of the LCD mode
register).
1/2 bias
V
L3
=V
LCD
V
L2
=V
L1
=1/2 V
LCD
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
V
CC
V
CC
PX
X