ADE5166 datasheet(104/156 Pages) AD

104 / 156 page

ADE5166/ADE5169/ADE5566/ADE5569

Rev. B | Page 104 of 156

Writing to LCD Data Registers

To update the LCD data memory, first set the LSB of the LCD

Configuration Y SFR (LCDCONY, Address 0xB1) to freeze the

data being displayed on the LCD while updating it. This operation

ensures that the data displayed on the screen does not change

while the data is being changed. Then, move the data to the LCD

data SFR (LCDDAT, Address 0xAE) prior to accessing the LCD

pointer SFR (LCDPTR, Address 0xAC). The address of the LCD

screen should be consistent with the data changed. When the MSB

of the LCD pointer SFR (LCDPTR, Address 0xAC) is set, the

contents of the LCD data SFR (LCDDAT, Address 0xAE) are

transferred to the internal LCD data memory designated by the

address in the LCD pointer SFR (LCDPTR, Address 0xAC) and

the screen designator. Clear the LSB of the LCD Configuration Y

SFR (LCDCONY, Address 0xB1) when all of the data memory has

been updated to allow the use of the new LCD setup for display.

Sample 8052 code to update the segments attached to Pin FP10

and Pin FP11 on Screen 1 is as follows:

ORL

LCDCONY,#01h

;start updating the data

MOV

LCDDAT,#FFh

MOV

LCDPTR,#80h OR 05h

ANL

LCDCONY,#0FEh ;update finished

Reading LCD Data Registers

When the MSB of the LCD pointer SFR (LCDPTR, Address 0xAC)

is cleared, the contents of the LCD data memory of the correspond-

ing screen designated by LCDPTR are transferred to the LCD

data SFR (LCDDAT, Address 0xAE).

Sample 8052 code to read the contents of LCD Data Memory

Address 0x07 on Screen 1, which holds the on and off state of

the segments attached to FP14 and FP15, is as follows:

MOV

LCDPTR,#07h

MOV

R1, LCDDAT

VOLTAGE GENERATION

The ADE5166/ADE5169/ADE5566/ADE5569 provide two ways

to generate the LCD waveform voltage levels. The on-chip charge

pump option can generate 5 V. This makes it possible to use 5 V

LCDs with the 3.3 V ADE5166/ADE5169/ADE5566/ADE5569.

There is also an option to use an external resistor ladder with a

3.3 V LCD. The EXTRES bit (Bit 6) in the LCD Configuration X

SFR (LCDCONX, Address 0x9C) selects the resistor ladder or

charge pump option.

When selecting how to generate the LCD waveform voltages,

the following should be considered:

•

Lifetime performance power consumption

•

Contrast control

Lifetime Performance Power Consumption

In most LCDs, a high amount of current is required when the LCD

waveforms change state. The external resistor ladder option draws a

constant amount of current, whereas the charge pump circuitry

allows dynamic current consumption. If the LCD module is used

with the internal charge pump option when the display is disabled,

the voltage generation is disabled so that no power is consumed by

the LCD function. This feature results in significant power

savings if the display is turned off during battery operation.

Contrast Control

The electrical characteristics of the liquid in the LCD change

over temperature. This requires adjustments in the LCD waveform

voltages to ensure a readable display. An added benefit of the

internal charge pump voltage generation is a configurable bias

voltage that can be compensated over temperature and supply

to maintain contrast on the LCD. These compensations can be

performed based on the ADE5166/ADE5169/ADE5566/

ADE5569 temperature and supply voltage measurements (see

the Temperature, Battery, and Supply Voltage Measurements

section). This dynamic contrast control is not easily imple-

mented with external resistor ladder voltage generation.

The LCD bias voltage sets the contrast of the display when the

charge pump provides the LCD waveform voltages. The ADE5166/

ADE5169/ADE5566/ADE5569 provide 64 bias levels selected by

the BIASLVL bits (Bits[5:0]) in the LCD Configuration X SFR

(LCDCONX, Address 0x9C). The voltage level on LCDVA,

LCDVB, and LCDVC depends on the internal voltage reference

value (VREF), BIASLVL selection, and the biasing selected, as

described in Table 93.

Lifetime Performance

DC offset on a segment degrades its performance over time.

The voltages generated through the internal charge pump

switch faster than those generated by the external resistor

ladder, reducing the likelihood of a dc voltage being applied

to a segment and increasing the lifetime of the LCD.

LCD EXTERNAL CIRCUITRY

The voltage generation selection is made by the EXTRES bit

(Bit 6) in the LCD Configuration X SFR (LCDCONX,

Address 0x9C). This bit is cleared by default for charge pump

voltage generation, but it can be set to enable an external

resistor ladder.

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