2010-2013 Microchip Technology Inc. DS30009740B-page 9
Liquid Crystal Display (LCD)
5.0 LCD BIAS TYPES
The LCD module can be configured in one of three Bias types:
• Static Bias (Two Voltage Levels: V
SS and VDD)
• 1/2 Bias (Three Voltage Levels: VSS, 1/2 VDD and VDD)
• 1/3 Bias (Four Voltage Levels: VSS, 1/3 VDD, 2/3 VDD and VDD)
LCD Bias voltages can be generated with an internal resistor ladder, internal Bias generator or
external resistor ladder.
5.1 Internal Resistor Biasing
This mode does not use external resistors, but rather internal resistor ladders that are configured
to generate the Bias voltage.
The internal reference ladder actually consists of three separate ladders. Disabling the internal
reference ladder disconnects all of the ladders, allowing external voltages to be supplied.
Depending on the total resistance of the resistor ladders, the biasing can be classified as low,
medium or high power.
Table 5-1 shows the total resistance of each of the ladders. Figure 5-1 shows the internal resister
ladder connections. When the internal resistor ladder is selected, the Bias voltage will be internal;
it can also provide software contrast control (using LCDCST<2:0>).
Table 5-1: Internal Resistance Ladder Power Modes
Power Mode
Nominal
Resistance of
Entire Ladder
I
DD
Low 3 MΩ 1 µA
Medium 300 kΩ 10 µA
High 30 kΩ 100 µA
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