PIC16F877T-20I/L Microchip Technology, PIC16F877T-20I/L Datasheet - Page 212

• Manufacturer Part Number: PIC16F877T-20I/L
• Description: IC MCU FLASH 8KX14 EE 44PLCC
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F877T-20I/L

• 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: 33
• Program Memory Size: 14KB (8K x 14)
• Program Memory Type: FLASH
• Eeprom Size: 256 x 8
• Ram Size: 368 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: External
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 44-PLCC
• For Use With: DVA16XL441 - ADAPTER DEVICE ICE 44PLCC309-1040 - ADAPTER 44-PLCC ZIF TO 40-DIP309-1039 - ADAPTER 44-PLCC TO 40-DIP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PICmicro MID-RANGE MCU FAMILY
14.5.2.2
DS31014A-page 14-10
Minimum Resolution
The minimum resolution (in time) of each bit of the PWM duty cycle depends on the prescaler of
Timer2.
Table 14-4: Minimum Duty Cycle Bit Time
Example 14-2:
At most, an 8-bit resolution duty cycle can be obtained from a 78.125 kHz frequency and a
20 MHz oscillator, i.e., 0 DCxB9:DCxB0 255. Any value greater than 255 will result in a 100%
duty cycle.
In order to achieve higher resolution, the PWM frequency must be decreased. In order to achieve
higher PWM frequency, the resolution must be decreased.
Table 14-5
caler and PR2 values are also shown.
Table 14-5: Example PWM Frequencies and Bit Resolutions at 20 MHz
Desired PWM frequency is 78.125 kHz,
Fosc = 20 MHz
TMR2 prescale = 1
Find the maximum resolution of the duty cycle that can be used with a 78.125 kHz frequency
and 20 MHz oscillator:
Timer Prescaler
(1, 4, 16)
PR2 Value
Maximum
Resolution (bits)
PWM Frequency
Prescaler
1/78.125 kHz= [(PR2) + 1] • 4 • 1/20 MHz • 1
12.8 s = [(PR2) + 1] • 4 • 50 ns • 1
PR2
1/78.125 kHz= 2
12.8 s = 2
256
log(256) = (PWM Resolution) • log(2)
8.0
Value
16
1
4
lists example PWM frequencies and resolutions for Fosc = 20 MHz. The TMR2 pres-
= 63
= 2
= PWM Resolution
PWM RESOLUTION
PWM RESOLUTION
PWM Period and Duty Cycle Calculation
T2CKPS1:T2CKPS0
PWM RESOLUTION
1.22 kHz
0xFF
16
10
0 0
0 1
1 x
• 50 ns • 1
4.88 kHz
• 1/20 MHz • 1
0xFF
10
4
19.53 kHz
Minimum Resolution
0xFF
10
1
(Time)
4 T
T
T
OSC
CY
CY
78.12 kHz
0x3F
1
8
1997 Microchip Technology Inc.
156.3 kHz
0x1F
1
7
208.3 kHz
0x17
5.5
1