DSPIC30F2010 datasheet(85/236 Pages) MICROCHIP

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DS70135E-page 83

dsPIC30F4011/4012

13.4.2

PWM PERIOD

The PWM period is specified by writing to the PRx

Equation 13-1.

EQUATION 13-1:

PWM PERIOD

PWM frequency is defined as 1/[PWM period].

When the selected TMRx is equal to its respective

Period register, PRx, the following four events occur on

the next increment cycle:

• TMRx is cleared.

• The OCx pin is set.

- Exception 1: If PWM duty cycle is 0x0000,

the OCx pin will remain low.

- Exception 2: If duty cycle is greater than PRx,

the pin will remain high.

• The PWM duty cycle is latched from OCxRS into

OCxR.

• The corresponding timer interrupt flag is set.

See Figure 13-1 for key PWM period comparisons.

Timer3 is referred to in the figure for clarity.

FIGURE 13-1:

PWM OUTPUT TIMING

13.5

Output Compare Operation During

CPU Sleep Mode

When the CPU enters the Sleep mode, all internal

clocks are stopped. Therefore, when the CPU enters

the Sleep state, the output compare channel will drive

the pin to the active state that was observed prior to

entering the CPU Sleep state.

For example, if the pin was high when the CPU

entered the Sleep state, the pin will remain high. Like-

wise, if the pin was low when the CPU entered the

Sleep state, the pin will remain low. In either case, the

output compare module will resume operation when

the device wakes up.

13.6

Output Compare Operation During

CPU Idle Mode

When the CPU enters the Idle mode, the output

compare module can operate with full functionality.

The output compare channel will operate during the

CPU Idle mode if the OCSIDL bit (OCxCON<13>) is at

logic ‘0’ and the selected time base (Timer2 or Timer3)

is enabled and the TSIDL bit of the selected timer is

set to logic ‘0’.

13.7

Output Compare Interrupts

The output compare channels have the ability to gener-

ate an interrupt on a compare match for whichever

Match mode has been selected.

For all modes except the PWM mode, when a compare

event occurs, the respective interrupt flag (OCxIF) is

asserted and an interrupt will be generated if enabled.

The OCxIF bit is located in the corresponding IFSx reg-

ister, and must be cleared in software. The interrupt is

enabled via the respective Compare Interrupt Enable

(OCxIE) bit, located in the corresponding IECx register.

For the PWM mode, when an event occurs, the respec-

tive Timer Interrupt Flag (T2IF or T3IF) is asserted and

an interrupt will be generated if enabled. The TxIF bit is

located in the IFS0 register and must be cleared in

software. The interrupt is enabled via the respective

Timer Interrupt Enable bit (T2IE or T3IE) located in the

IEC0 register. The output compare interrupt flag is

never set during the PWM mode of operation.

PWM period = [(PRx) + 1] • 4 • TOSC •

(TMRx prescale value)

Period

Duty Cycle

TMR3 = Duty Cycle (OCxR)

TMR3 = PR3

T3IF = 1

(Interrupt Flag)

OCxR = OCxRS

TMR3 = PR3

(Interrupt Flag)

OCxR = OCxRS

T3IF = 1

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