W742E Datasheet, PDF (46/60 Pages) Winbond – 4 BIT MICROCONTROLLER

W742E/C811
5.25.2 LCD voltage and contrast adjusting
LCD power (VLCD2) has two source, one is directly from the VLCD1 pin, another is from internal pump
circuit. The LCD power source is selected by mask option. The pump circuit doubles the µC input
voltage (VDD), the power consumption in internal pump mode is more than directly input from
VLCD1. The LCD pump circuit only works in the VDD range from 2.4V to 4.0V. If the operating voltage
of VDD is up 4.0V, the LCD power should come from the VLCD1 pin. The LCD contrast is adjustable
by an internal variable resistor (VR). VLCD voltage is controlled by setting bit2, bit1 and bit0 of LCD
contrast control register (LCDCC). LCDCC is determined by executing MOV LCDCC,#I. The Figure 5-
18 shows the LDC power control as below:
VDD
outside chip
inside chip
VLCD1
Internal
CP
Pump
Circuit
CN
EN
STOP
LCDOFF
Code Option
S1
VLCD2
VR
R
R
R
R
R
Note: VR is determined by LCDCC register
Figure 5-18 LCD power control circuit
VLCD
V1
V2
V3
V4
VSS
3
LCDCC
2
1
0
W
W
W
Note: W means write only.
LCDCC
0000H
0001H
0010H
0011H
0100H
0101H
0110H
0111H
Bit 3 is reserved.
VLCD/VLCD2
1.00
0.96
0.93
0.89
0.86
0.81
0.76
0.71
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