DSPIC30F2010 datasheet(86/204 Pages) MICROCHIP

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dsPIC30F2010

DS70118H-page 86

14.1.4

DOUBLE UPDATE MODE

In the Double Update mode (PTMOD<1:0> = 11), an

interrupt event is generated each time the PTMR

match occurs. The postscaler selection bits have no

effect in this mode of the timer.

The Double Update mode provides two additional

functions to the user. First, the control loop bandwidth

is doubled because the PWM duty cycles can be

updated, twice per period. Second, asymmetrical

center-aligned PWM waveforms can be generated,

which are useful for minimizing output waveform

distortion in certain motor control applications.

14.1.5

PWM TIME BASE PRESCALER

The input clock to PTMR (FOSC/4), has prescaler

options of 1:1, 1:4, 1:16 or 1:64, selected by control bits

PTCKPS<1:0> in the PTCON SFR. The prescaler

counter is cleared when any of the following occurs:

• a write to the PTMR register

• a write to the PTCON register

• any device Reset

The PTMR register is not cleared when PTCON is

written.

14.1.6

PWM TIME BASE POSTSCALER

The match output of PTMR can optionally be

post-scaled through a 4-bit postscaler (which gives a

1:1 to 1:16 scaling).

The postscaler counter is cleared when any of the

following occurs:

• a write to the PTMR register

• a write to the PTCON register

• any device Reset

The PTMR register is not cleared when PTCON is

written.

14.2

PWM Period

PTPER is a 15-bit register and is used to set the

counting period for the PWM time base. PTPER is a

double-buffered register. The PTPER buffer contents

are loaded into the PTPER register at the following

instances:

• Free Running and Single Shot modes: When the

PTMR register is reset to zero after a match with

the PTPER register.

• Up/Down Counting modes: When the PTMR

The value held in the PTPER buffer is automatically

loaded into the PTPER register when the PWM time

base is disabled (PTEN = 0).

The

PWM

period

can

determined

using

Equation 14-1:

EQUATION 14-1:

PWM PERIOD

If the PWM time base is configured for one of the

Up/Down Count modes, the PWM period is found using

Equation 14-2.

EQUATION 14-2:

PWM PERIOD (UP/DOWN

COUNT MODE)

The maximum resolution (in bits) for a given device

oscillator and PWM frequency can be determined using

Equation 14-3:

EQUATION 14-3:

PWM RESOLUTION

Note:

Programming a value of 0x0001 in the

period

could

generate

continuous interrupt pulse, and hence,

must be avoided.

TPWM =

TCY

• (PTPER + 1)

(PTMR Prescale Value)

TPWM =

TCY

• 2 • (PTPER + 0.75)

(PTMR Prescale Value)

Resolution =

log (2

• TPWM / TCY)

log (2)

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