PIC18F6621-I/PT Microchip Technology Inc., PIC18F6621-I/PT Datasheet - Page 156

• Manufacturer Part Number: PIC18F6621-I/PT
• Description: 64 PIN, 64 KB FLASH, 3840 RAM, 52 I/O
• Manufacturer: Microchip Technology Inc.

Specifications of PIC18F6621-I/PT

• A/d Inputs: 12-Channel, 10-Bit
• Comparators: 2
• Cpu Speed: 10 MIPS
• Eeprom Memory: 1024 Bytes
• Input Output: 54
• Interface: I2C/SPI/UART/USART
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 64-pin TQFP
• Programmable Memory: 64K Bytes
• Ram Size: 3.8K Bytes
• Speed: 40 MHz
• Timers: 2-8-bit, 3-16-bit
• Voltage, Range: 2-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

PIC18F6525/6621/8525/8621
16.4
In Pulse-Width Modulation (PWM) mode, the CCP4 pin
produces up to a 10-bit resolution PWM output. Since
the CCP4 pin is multiplexed with the PORTG data
latch, the TRISG<3> bit must be cleared to make the
CCP4 pin an output.
Figure 16-4 shows a simplified block diagram of the
CCP module in PWM mode.
For a step-by-step procedure on how to set up the CCP
module for PWM operation, see Section 16.4.3
“Setup for PWM Operation”.
FIGURE 16-4:
A PWM output (Figure 16-5) has a time base (period)
and a time that the output stays high (duty cycle).
The frequency of the PWM is the inverse of the
period (1/period).
FIGURE 16-5:
DS39612B-page 154
Note 1:
Note:
CCPR4H (Slave)
CCPR4L
Comparator
Duty Cycle Registers
TMR2
TMR2 = PR2
PR2
Comparator
PWM Mode
8-bit TMR2 or TMR4 is concatenated with 2-bit
Duty Cycle
internal Q clock, or 2 bits of the prescaler, to create
10-bit time base.
Clearing the CCP4CON register will force
the CCP4 PWM output latch to the default
low level. This is not the PORTG I/O data
latch.
Period
(Note 1)
TMR2 = Duty Cycle
Clear Timer,
CCP1 pin and
latch D.C.
SIMPLIFIED PWM BLOCK
DIAGRAM
PWM OUTPUT
TMR2 = PR2
CCP1CON<5:4>
R
S
Q
TRISG<3>
RG3/CCP4
16.4.1
The PWM period is specified by writing to the PR2
(PR4) register. The PWM period can be calculated
using the following formula:
EQUATION 16-1:
PWM frequency is defined as 1/[PWM period].
When TMR2 (TMR4) is equal to PR2 (PR2), the
following three events occur on the next increment
cycle:
• TMR2 (TMR4) is cleared
• The CCP4 pin is set (exception: if PWM duty
• The PWM duty cycle is latched from CCPR4L into
16.4.2
The PWM duty cycle is specified by writing to the
CCPR4L register and to the CCP4CON<5:4> bits. Up
to 10-bit resolution is available. The CCPR4L contains
the eight MSbs and the CCP4CON<5:4> contains the
two LSbs. This 10-bit value is represented by
CCPR4L:CCP4CON<5:4>. The following equation is
used to calculate the PWM duty cycle in time:
EQUATION 16-2:
CCPR4L and CCP4CON<5:4> can be written to at any
time, but the duty cycle value is not latched into
CCPR4H until after a match between PR2 and TMR2
occurs (i.e., the period is complete). In PWM mode,
CCPR4H is a read-only register.
The CCPR4H register and a 2-bit internal latch are
used to double-buffer the PWM duty cycle. This
double-buffering is essential for glitchless PWM
operation.
When the CCPR4H and 2-bit latch match TMR2, con-
catenated with an internal 2-bit Q clock or 2 bits of the
TMR2 prescaler, the CCP4 pin is cleared.
PWM Duty Cycle = (CCPR4L:CCP4CON<5:4>) •
cycle = 0%, the CCP4 pin will not be set)
CCPR4H
Note:
PWM Period = [(PR2) + 1] • 4 • T
PWM PERIOD
The Timer2 and Timer4 postscalers (see
Section 13.0 “Timer2 Module”) are not
used in the determination of the PWM
frequency. The postscaler could be used
to have a servo update rate at a different
frequency than the PWM output.
PWM DUTY CYCLE
T
(TMR2 Prescale Value)
 2005 Microchip Technology Inc.
OSC
• (TMR2 Prescale Value)
OSC
•