PIC16F1946 datasheet(349/448 Pages) MICROCHIP

349 / 448 page

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Preliminary

DS41414C-page 349

PIC16(L)F1946/1947

27.5.4

CONTRAST CONTROL

The LCD contrast control circuit consists of a

seven-tap resistor ladder, controlled by the LCDCST

bits. Refer to Figure 27-7.

The contrast control circuit is used to decrease the

output voltage of the signal source by a total of

approximately 10%, when LCDCST = 111.

Whenever the LCD module is inactive (LCDA = 0), the

contrast control ladder will be turned off (open).

FIGURE 27-7:

INTERNAL REFERENCE AND CONTRAST CONTROL BLOCK DIAGRAM

27.5.5

INTERNAL REFERENCE

Under firmware control, an internal reference for the

LCD bias voltages can be enabled. When enabled, the

source of this voltage can be either VDDIO or a voltage

3 times the main fixed voltage reference (3.072V).

When no internal reference is selected, the LCD con-

trast control circuit is disabled and LCD bias must be

provided externally.

Whenever the LCD module is inactive (LCDA = 0), the

internal reference will be turned off.

When the internal reference is enabled and the Fixed

Voltage Reference is selected, the LCDIRI bit can be

used to minimize power consumption by tieing into the

LCD reference ladder automatic power mode switching.

When LCDIRI = 1 and the LCD reference ladder is in

Power mode ‘B’, the LCD internal FVR buffer is

disables.

27.5.6

VLCD<3:1> PINS

The VLCD<3:1> pins provide the ability for an external

LCD bias network to be used instead of the internal lad-

der. Use of the VLCD<3:1> pins does not prevent use

of the internal ladder. Each VLCD pin has an indepen-

dent control in the LCDREF register (Register 27-3),

allowing access to any or all of the LCD Bias signals.

This architecture allows for maximum flexibility in

different applications

For example, the VLCD<3:1> pins may be used to add

capacitors to the internal reference ladder, increasing

the drive capacity.

For applications where the internal contrast control is

insufficient, the firmware can choose to only enable the

VLCD3 pin, allowing an external contrast control circuit

to use the internal reference divider.

LCDCST<2:0>

Analog

7 Stages

MUX

To top of

Reference Ladder

3.072V

VDDIO

From FVR

Buffer

Internal Reference

Contrast control

Note:

The LCD module automatically turns on the

fixed voltage reference when needed.

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