Datasheet
PIC24FJ256GB110 FAMILY
DS39897C-page 176 2009 Microchip Technology Inc.
FIGURE 14-2: OUTPUT COMPARE BLOCK DIAGRAM (DOUBLE-BUFFERED, 16-BIT PWM MODE)
14.3.1 PWM PERIOD
The PWM period is specified by writing to PRy, the
Timer Period register. The PWM period can be
calculated using Equation 14-1.
EQUATION 14-1: CALCULATING THE PWM
PERIOD
(1)
14.3.2 PWM DUTY CYCLE
The PWM duty cycle is specified by writing to the
OCxRS and OCxR registers. The OCxRS and OCxR
registers can be written to at any time, but the duty
cycle value is not latched until a match between PRy
and TMRy occurs (i.e., the period is complete). This
provides a double buffer for the PWM duty cycle and is
essential for glitchless PWM operation.
Some important boundary parameters of the PWM duty
cycle include:
• If OCxR, OCxRS, and PRy are all loaded with
0000h, the OCx pin will remain low (0% duty
cycle).
• ·If OCxRS is greater than PRy, the pin will remain
high (100% duty cycle).
See Example 14-1 for PWM mode timing details.
Table 14-1 and Table 14-2 show example PWM
frequencies and resolutions for a device operating at
4 MIPS and 10 MIPS, respectively.
OCxR buffer
Comparator
OCxTMR
OCxCON1
OCxCON2
OC Output and
OCx Interrupt
OCx Pin
OCxRS buffer
Comparator
Fault Logic
Match
Match
Trigger and
Sync Logic
Clock
Select
Increment
Reset
OC Clock
Sources
Trigger and
Sync Sources
Reset
Match Event
OCFA/OCFB
OCTSELx
SYNCSELx
TRIGSTAT
TRIGMODE
OCTRIG
OCMx
OCINV
OCTRIS
FLTOUT
FLTTRIEN
FLTMD
ENFLT0
OCFLT0
OCxR
OCxRS
Event
Event
Rollover
Rollover/Reset
Rollover/Reset
Note 1: The OCx outputs must be assigned to an available RPn pin before use. Please see Section 10.4 “Peripheral
Pin Select” for more information.
Note: A PRy value of N will produce a PWM
period of N + 1 time base count cycles. For
example, a value of 7 written into the PRy
register will yield a period consisting of
8 time base cycles.
PWM Period = [(PRy) + 1] • TCY • (Timer Prescale Value)
PWM Frequency = 1/[PWM Period]
where:
Note 1: Based on T
CY = TOSC * 2, Doze mode
and PLL are disabled.