Datasheet

Data Sheet ADE5166/ADE5169/ADE5566/ADE5569
Rev. D | Page 105 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 (V
REF
), 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.