PIC16F1938_13 Datasheet, PDF (334/488 Pages) Microchip Technology – 28/40/44-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver

PIC16(L)F1938/9
27.5 LCD Bias Internal Reference
Ladder
The internal reference ladder can be used to divide the
LCD bias voltage two or three equally spaced voltages
that will be supplied to the LCD segment pins. To create
this, the reference ladder consists of three matched
resistors. Refer to Figure 27-3.
27.5.1 BIAS MODE INTERACTION
When in 1/2 Bias mode (BIASMD = 1), then the middle
resistor of the ladder is shorted out so that only two
voltages are generated. The current consumption of the
ladder is higher in this mode, with the one resistor
removed.
TABLE 27-3: LCD INTERNAL LADDER
POWER MODES (1/3 BIAS)
Power
Mode
Nominal Resistance of Nominal
Entire Ladder
IDD
Low
Medium
High
3 Mohm
300 kohm
30 kohm
1 µA
10 µA
100 µA
27.5.2 POWER MODES
The internal reference ladder may be operated in one of
three power modes. This allows the user to trade off LCD
contrast for power in the specific application. The larger
the LCD glass, the more capacitance is present on a
physical LCD segment, requiring more current to
maintain the same contrast level.
Three different power modes are available, LP, MP and
HP. The internal reference ladder can also be turned off
for applications that wish to provide an external ladder
or to minimize power consumption. Disabling the
internal reference ladder results in all of the ladders
being disconnected, allowing external voltages to be
supplied.
Whenever the LCD module is inactive (LCDA = 0), the
internal reference ladder will be turned off.
DS40001574C-page 334
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