PIC18F87K90 Datasheet, PDF (279/566 Pages) Microchip Technology – 64/80-Pin, High-Performance Microcontrollers with LCD Driver and nanoWatt XLP Technology

PIC18F87K90 FAMILY
20.3 LCD Bias Types
The LCD module can be configured in one of three bias
types:
• Static bias (two voltage levels: VSS 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 or
external resistor ladder. The internal resistor ladder
eliminates the external solution’s use of up to three
pins.
If the internal reference ladder is used to generate bias
voltages, it also can provide software contrast control
(using LCDCST<2:0>). An external resistor ladder can
not do this.
20.3.1 EXTERNAL RESISTOR BIASING
The external resistor ladder should be connected to the
VLCD1 pin (Bias 1), VLCD2 pin (Bias 2), VLCD3 pin
(Bias 3) and VSS. The VLCD3 pin is used to set the
highest voltage to the LCD glass and can be connected
to VDD or a lower voltage.
Figure 20-3 shows the proper way to connect the
resistor ladder to the Bias pins.
FIGURE 20-3:
LCD BIAS EXTERNAL RESISTOR LADDER CONNECTION DIAGRAM
VLCD3
VLCD2
VLCD1
VLCD0
To
LCD
Driver
VLCD0
VLCD1
VLCD2
VLCD3
Static
Bias
AVSS
—
—
AVDD
1/2 Bias 1/3 Bias
AVSS
AVSS
1/2 AVDD 1/3 AVDD
1/2 AVDD 2/3 AVDD
AVDD
AVDD
AVDD*
LCD Bias 3 LCD Bias 2 LCD Bias 1
AVDD*
10 k*
10 k*
AVDD*
10 k*
10 k*
10 k*
Connections for External R-ladder
Static Bias
AVSS
1/2 Bias
AVSS
1/3 Bias
* These values are provided for design guidance only and should be optimized for the application by the designer.
 2010 Microchip Technology Inc.
Preliminary
DS39957B-page 279