
Mitsubishi microcomputers
M30220 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
LCD Drive Control Circuit
126
Charge-pump
The charge-pump performs threefold boosting. This circuit inputs a reference voltage for boosting from
LCD power input pin VL1.
To activate the charge-pump, by the segment output enable register and the LCD mode register, choose
the segment/port, select the time division and the bias control, and set up the LCD frame frequency
counter, and select the count source for LCDCK, then set the LCD output enable bit (bit 7 at the address
012216) to “enable”, apply a voltage equal to or greater than 1.3 V but not exceeding 2.1 V to the VL1 pin,
after that, set the charge-pump control bit (bit 4 at address 012016) to “step up enabled”. However, set the
bias control to “1/3 bias” without fail.
When using the charge-pump, a voltage that is twice as large as VL1 occurs at VL2 pin, and a voltage that
is three times as large as VL1 occurs at the VL3 pin.
The charge-pump control bit (bit 4 of the address 012016) controls the charge-pump.
When not using the charge-pump, enable the LCD output enable bit and apply an appropriate voltage to
the LCD power supply input pins (VL1 to VL3). When the LCD output enable bit is disabled, the VL3 pin is
connected to VCC internally.
Bias Control and Applied Voltage to LCD Power Input Pins
To the LCD power input pins (VL1 to VL3), apply the voltage shown in Table 1.16.2 according to the bias value.
Select a bias value by the bias control bit (bit 2 of the address 012016).
Table 1.16.2. Bias control and applied voltage to VL1 to VL3
Bias value
Voltage value
VL3 = VLCD
1/3 bias
VL2 = 2/3 VLCD
VL1 = 1/3 VLCD
1/2 bias
VL3 = VLCD
VL2 = VL1 = 1/2 VLCD
Note : VLCD is the maximum value of supplied voltage for the LCD panel.
Figure 1.16.3. Example of circuit at each bias
VL3
VL2
C2
C1
VL1
1/3 bias
when using the charge-pump
VL3
VL2
C2
C1
VL1
1/3 bias
when not using the charge-pump
Open
R2
R1
R3
R1=R2=R3
Contrast control
VL3
VL2
C2
C1
VL1
1/2 bias
Open
R4
R5
R4=R5
Contrast control
When selecting output port function
(not using LCD panel)
VL1
VL3
VL2
C1
C2
Open
VLCD
VCC
When not using the charge-pump