ADE75 datasheet(100/148 Pages) AD

100 / 148 page

ADE75xx/ADE71xx

Preliminary Technical Data

Rev. PrE | Page 100 of 148

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 bit EXTRES in the

LCD Configuration X SFR (LCDCONX, 0x9C). This bit is clear

by default for charge pump voltage generation but can be set to

enable an external resistor ladder.

Charge Pump:

Voltage generation through the charge pump requires external

capacitors to store charge. The external connections to VA, VB,

and VC as well as VP1 and VP2 are shown in LCD

Configuration X SFR (LCDCONX, 0x9C).

LCDVA

LCDVB

LCDVC

LCDVP1

LCDVP2

Charge Pump

and

LCD Waveform

Circuitry

470nF

100nF

Figure 63: External circuitry for Charge Pump option

External Resistor Ladder:

To enable the external resistor ladder option, set the EXTRES

bit in the LCD Configuration X SFR (LCDCONX, 0x9C). When

EXTRES=1, the LCD waveform voltages are supplied by the

external resistor ladder. Since the LCD voltages are not being

generated on-chip, the LCD bias compensation implemented to

maintain contrast over temperature and supply is not possible.

The external circuitry needed for the resistor ladder option is

shown in Figure 64. The resistors required should be in the

range of 10k to 100k and based on the current required by the

LCD being used.

LCDVA

LCDVB

LCDVC

LCDVP1

LCDVP2

LCD Waveform

Circuitry

Figure 64: External circuitry for External Resistor Ladder option

LCD FUNCTION IN PSM2

The LCDPSM2 bit in the LCD Configuration SFR (LCDCON,

0x95) and the LCDEN bit in the LCD Configuration SFR

(LCDCON, 0x95) control LCD functionality in the PSM2

operating mode. The voltage reference must be enabled during

battery mode for the charge pump voltage generation to work.

Ensure this by setting REF_BAT_EN in the Peripheral

Configuration SFR (PERIPH, 0xF4).

LCDPSM2

LCDEN

Comments

The display is OFF in PSM2.

The display is ON in PSM2.

The display is OFF in PSM2.

Note that the LCD configuration and data memory is retained

when the display is turned off.

EXAMPLE LCD SETUP

An example to set up the LCD peripheral for a specific LCD is

described below.

Type of LCD: 5V, 4x multiplexed with 1/3 bias, 96 segments

Voltage Generation: Internal Charge Pump

Refresh Rate: 64Hz

A 96 segment LCD with 4x multiplexing requires 96/4=24

segment lines. There are 16 pins that automatically dedicated

for use as LCD segments, FP0 to FP15. Eight more pins must be

chosen for the LCD function. Since the LCD has 4x

multiplexing, all four common lines are used so COM2/FP28

and COM3/FP27 cannot be utilized as segment lines. Based on

the alternate functions of the pins used for FP16 through FP25,

FP16-23 are chosen for the seven remaining segment lines.

These pins will be enabled for LCD functionality in the LCD

Segment Enable SFR (LCDSEGE, 0x97) and LCD Segment

Enable 2 SFR (LCDSEGE2, 0xED).

To determine contrast setting for this 5V LCD, look in Table 76

to find the BIASLVL[5:0] setting that corresponds to a VC of 5V

in 1/3 Bias Mode. The nominal bias level setting for this LCD is

BIASLVL[5:0]=[111111].

The LCD is setup with the following 8052 code:

; setup LCD pins to have LCD functionality

MOV

LCDSEGE, # 00111100b

MOV

LCDSEGE2, #00001111b

; setup LCDCON for fLCDCLK=2048Hz, 1/3 bias and 4x multiplexing

MOV

LCDCON, #00000111b

; setup LCDCONX for charge pump and BIASLVL[110111]

MOV

LCDCONX, #00110111b

; set up refresh rate for 64Hz with fLCDCLK=2048Hz, from

Table 79

MOV

LCDCLK, #00000011b

; set up LCD data registers with data to be displayed using

; LCDPTR and LCDDATA registers

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