Technical information

33
MITSUBISHI MICROCOMPUTERS
3820 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
Bias Control and Applied Voltage to LCD
Power Input Pins
To the LCD power input pins (VL1–VL3), apply the voltage shown in
Table 3 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 (COM0–COM3) 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. 25 Example of circuit at each bias
Table 3. Bias control and applied voltage to VL1–VL3
Bias value
1/3 bias
1/2 bias
Voltage value
VL3=VLCD
VL2=2/3 VLCD
VL1=1/3 VLCD
VL3=VLCD
VL2=VL1=1/2 VLCD
Note 1 :VLCD is the maximum value of supplied voltage for the
LCD panel.
Table 4. Duty ratio control and common pins used
Duty
ratio
2
3
4
Common pins used
Notes 1 : COM
2 and COM3 are open
2 : COM3 is open
Bit 1
0
1
1
Bit 0
1
0
1
COM
0, COM1 (Note 1)
COM
0–COM2 (Note 2)
COM
0–COM3
Duty ratio selection bit
V L3
V L2
V L1
R4
R5
R4 = R5
Contrast control
1/2 bias
V L3
V L2
V L1
Contrast control
R1
R2
R3
R1 = R2 = R3
1/3 bias