M38265EBGP datasheet(84/91 Pages) RENESAS

84 / 91 page

Rev.1.00

Sep 06, 2006

page 84 of 88

REJ03B0181-0100

3826 Group (One Time PROM version)

3.3.11 Notes on LCD drive control circuit

(1)

Count source for LCDCK

The LCDCK count source selection bit (bit 7 of LCD mode register (address 3916)) is set to “0”

after reset, selecting f(XCIN)/32. The sub clock has stopped after reset. Therefore, turn on LCD

after starting the oscillation and stabilizing the oscillation. Select the LCDCK count source after the

corresponding clock source becomes stable.

(2)

STP instruction

When executing the STP instruction, execute the STP instruction after setting the LCD enable bit

to “0”. If the STP instruction is executed during LCD lighting, direct-current voltage will be applied

to the LCD panel.

(3)

When not using LCD

When not using an LCD, leave the LCD segment and common pins open. Connect the VL1 pin to

Vss, and the VL2 and VL3 pins to Vcc.

(4)

Using voltage multiplier circuit

When using the voltage multiplier, apply the limit voltage or less to the VL1 pin, then set the voltage

multiplier control bit to “1” (enabled). If above the limit voltage is applied to the VL1 pin, current

may flow in the voltage multiplier circuit at the time of the voltage multiplier circuit operation start.

For the limit value, refer to “Electrical characteristics”.

When not using the voltage multiplier, set the LCD output enable bit to “1”, then apply proper

voltage to the LCD power input pins (VL1–VL3).

When the LCD output enable bit is set to “0” (disabled), the Vcc voltage is applied to the VL3 pin

inside of this microcomputer.

(5)

LCD drive power supply

Power supply capacitor may be insufficient with the division resistance for LCD power supply, and

the characteristic of the LCD panel. In this case, there is the method of connecting the bypass

capacitor about 0.1–0.33 µF to VL1–VL3 pins. The example of a strengthening measure of the LCD

drive power supply is shown in Figure 3.3.9.

Fig. 3.3.9 Strengthening measure example of LCD drive power supply

VL3

VL2

VL1

•Connect by the shortest possible wiring.

•Connect the bypass capacitor to the VL1–VL3 pins

as short as possible.

(Referential value: 0.1–0.33 µF)

3826 group

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