PIC16F87-I/SS Microchip Technology, PIC16F87-I/SS Datasheet - Page 478

• Manufacturer Part Number: PIC16F87-I/SS
• Description: IC MCU FLASH 4KX14 EEPROM 20SSOP
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F87-I/SS

• Program Memory Type: FLASH
• Program Memory Size: 7KB (4K x 14)
• Package / Case: 20-SSOP
• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 16
• Eeprom Size: 256 x 8
• Ram Size: 368 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Processor Series: PIC16F
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 368 B
• Interface Type: SSP/USART
• Maximum Clock Frequency: 20 MHz
• Number Of Programmable I/os: 16
• Number Of Timers: 3
• Operating Supply Voltage: 2 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• 3rd Party Development Tools: 52715-96, 52716-328, 52717-734
• Development Tools By Supplier: PG164130, DV164035, DV244005, DV164005, PG164120, ICE2000, DM163014
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 10 bit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: XLT20SS-1 - SOCKET TRANSITION 18DIP 20SSOPAC164307 - MODULE SKT FOR PM3 28SSOP
• Data Converters: -
• 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