PIC16F872-E/SS Microchip Technology, PIC16F872-E/SS Datasheet - Page 478

• Manufacturer Part Number: PIC16F872-E/SS
• Description: IC,MICROCONTROLLER,8-BIT,PIC CPU,CMOS,SSOP,28PIN,PLASTIC
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F872-E/SS

• Rohs Compliant: YES
• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: I²C, SPI
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 22
• Program Memory Size: 3.5KB (2K x 14)
• Program Memory Type: FLASH
• Eeprom Size: 64 x 8
• Ram Size: 128 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Data Converters: A/D 5x10b
• Oscillator Type: External
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 28-SSOP
• Package: 28SSOP
• Device Core: PIC
• Family Name: PIC16
• Maximum Speed: 20 MHz
• Operating Supply Voltage: 5 V
• Data Bus Width: 8 Bit
• Number Of Programmable I/os: 22
• Interface Type: I2C/SPI
• On-chip Adc: 5-chx10-bit
• Number Of Timers: 3
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PICmicro MID-RANGE MCU FAMILY
25.11
DS31025A-page 25-20
LCD Voltage Generation
Among the many ways to generate LCD voltage, two methods stand out above the crowd:
• resistor ladder
• charge pump.
The resistor ladder method, shown in
ages. This method uses inexpensive resistors to create the multi-level LCD voltages. Regardless
of the number of pixels that are energized the current remains constant. The voltage at point V3
is typically tied to V
The resistance values are determined by two factors: display quality and power consumption.
Display quality is a function of the LCD drive waveforms. Since the LCD panel is a capacitive
load, the waveform is distorted due to the charging and discharging currents. This distortion can
be reduced by decreasing the value of resistance. However, this change increases the power
consumption due to the increased current now flowing through the resistors. As the LCD panel
increases in size, the resistance value must be decreased to maintain the image quality of the
display.
Sometimes the addition of parallel capacitors to the resistance can reduce the distortion caused
by charging/discharging currents. The capacitors act as charge storage to provide current as the
display waveform transitions. In general, R is 1 k
200 k .
Figure 25-10: Resistor Ladder
Figure 25-11: Resistor Ladder with Capacitors
CC
, either internally or externally.
Figure
V
V
V
V
3
2
1
0
25-10, is most commonly used for higher V
V
V
V
V
3
2
1
0
+5V
to 50 k
R
R
R
and the potentiometer is 5 k
R
R
R
C
C
C
1997 Microchip Technology Inc.
CC
volt-
to