Datasheet
RL78/L12 CHAPTER 14 LCD CONTROLLER/DRIVER
R01UH0330EJ0200 Rev.2.00 634
Dec 13, 2013
Caution The reference resistance “R” value for external resistance division is 10 kΩ to 1 MΩ. In addition, to
stabilize the voltage of the V
L1 to VL4 pins, connect a capacitor between each of pins VL1 to VL4 and
the GND pin as needed. The reference capacitance is about 0.47
μ
F but it depends on the LCD panel
used, the number of segment pins, the number of common pins, the frame frequency, and the
operating environment. Thoroughly evaluate these values in accordance with your system and
adjust and determine the capacitance.
14.8.2 Internal voltage boosting method
RL78/L12 contains an internal voltage boost circuit for generating LCD drive power supplies. The internal voltage boost
circuit and external capacitors (0.47
μ
F±30%) are used to generate an LCD drive voltage. Only 1/3 bias mode or 1/4 bias
mode can be set for the internal voltage boosting method.
The LCD drive voltage of the internal voltage boosting method can supply a constant voltage, regardless of changes in
V
DD, because it is a power supply separate from the main unit.
In addition, a contrast can be adjusted by using the LCD boost level control register (VLCD).
Table 14-11. LCD Drive Voltages (Internal Voltage Boosting Method)
Bias Method
LCD Drive Voltage Pin
1/3 Bias Method 1/4 Bias Method
VL4 3 × VL1 4 × VL1
VL3
−
3 × VL1
VL2 2 × VL1 2 × VL1
VL1 LCD reference voltage LCD reference voltage
Figure 14-23. Examples of LCD Drive Power Connections (Internal Voltage Boosting Method)
(a) 1/3 bias method (b) 1/4 bias method
V
L4
V
DD
V
L3
/P125
V
L2
C3C2 C4
2 V
L1
3 V
L1
CAPH
CAPL
C1
V
L1
Drive voltage
generator
V
L4
V
DD
V
L3
/P125
V
L2
C3C2 C4
CAPH
CAPL
C1
V
L1
4 V
L1
C5
2 V
L1
3 V
L1
Drive voltage
generator
Remark Use a capacitor with as little leakage as possible.
In addition, make C1 a nonpolar capacitor.