64GA106 datasheet(170/330 Pages) MICROCHIP

170 / 330 page

PIC24FJ256GA110 FAMILY

DS39905E-page 170

 2010 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(1)

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

Rollover

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

8 time base cycles.

PWM Period = [(PRy) + 1] • TCY • (Timer Prescale Value)

PWM Frequency = 1/[PWM Period]

where:

Note 1:

Based on TCY = TOSC * 2, Doze mode

and PLL are disabled.

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