PIC18F2331_07 Datasheet, PDF (195/400 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D

PIC18F2331/2431/4331/4431
17.5 PWM Period
The PWM period is defined by the PTPER register pair
(PTPERL and PTPERH). The PWM period has 12-bit
resolution by combining 4 LSBs of PTPERH and 8 bits
of PTPERL. PTPER is a double-buffered register used
to set the counting period for the PWM time base.
The PTPER register contents are loaded into the
PTPER register at the following times:
• Free-Running and Single-Shot modes: When the
PTMR register is reset to zero after a match with
the PTPER register.
• Continuous Up/Down Count modes: When the
PTMR register is zero. The value held in the
PTPER register is automatically loaded into the
PTPER register when the PWM time base is
disabled (PTEN = 0). Figure 17-9 and
Figure 17-10 indicate the times when the contents
of the PTPER register are loaded into the actual
PTPER register.
The PWM period can be calculated from the following
formulas:
EQUATION 17-1: PWM PERIOD FOR
FREE-RUNNING MODE
(PTPER + 1) x PTMRPS
TPWM =
FOSC/4
EQUATION 17-2: PWM PERIOD FOR
CONTINUOUS UP/DOWN
COUNT MODE
(2 x PTPER) x PTMRPS
TPWM =
FOSC
4
The PWM frequency is the inverse of period; or:
EQUATION 17-3: PWM FREQUENCY
PWM Frequency =
1
PWM Period
The maximum resolution (in bits) for a given device
oscillator and PWM frequency can be determined from
the following formula:
EQUATION 17-4: PWM RESOLUTION
FOSC
log _FPWM
Resolution =
log(2)
The PWM resolutions and frequencies are shown for a
selection of execution speeds and PTPER values in
Table 17-2. The PWM frequencies in Table 17-2 are
calculated for Edge-Aligned PWM mode. For
Center-Aligned mode, the PWM frequencies will be
approximately one-half the values indicated in this
table.
TABLE 17-2: EXAMPLE PWM FREQUENCIES
AND RESOLUTIONS
PWM Frequency = 1/TPWM
FOSC
MIPS
PTPER
Value
PWM
Resolution
PWM
Frequency
40 MHz 10 0FFFh 14 bits
2.4 kHz
40 MHz 10 07FFh 13 bits
4.9 kHz
40 MHz 10 03FFh 12 bits
9.8 kHz
40 MHz 10 01FFh 11 bits 19.5 kHz
40 MHz 10 FFh
10 bits 39.0 kHz
40 MHz 10 7Fh
9 bits
78.1 kHz
40 MHz 10 3Fh
8 bits 156.2 kHz
40 MHz 10 1Fh
7 bits 312.5 kHz
40 MHz 10 0Fh
6 bits
625 kHz
25 MHz 6.25 0FFFh 14 bits
1.5 kHz
25 MHz 6.25 03FFh 12 bits
6.1 kHz
25 MHz 6.25 FFh
10 bits 24.4 kHz
10 MHz 2.5 0FFFh 14 bits
610 Hz
10 MHz 2.5 03FFh 12 bits
2.4 kHz
10 MHz 2.5 FFh
10 bits
9.8 kHz
5 MHz 1.25 0FFFh 14 bits
305 Hz
5 MHz 1.25 03FFh 12 bits
1.2 kHz
5 MHz 1.25 FFh
10 bits
4.9 kHz
4 MHz 1 0FFFh 14 bits
244 Hz
4 MHz 1 03FFh 12 bits
976 Hz
4 MHz 1 FFh
10 bits
3.9 kHz
Note: For center-aligned operation, PWM frequencies
will be approximately 1/2 the value indicated in
the table.
© 2007 Microchip Technology Inc.
Preliminary
DS39616C-page 193