DSPIC30F3010 datasheet(101/228 Pages) MICROCHIP

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DS70141F-page 101

dsPIC30F3010/3011

15.3

Edge-Aligned PWM

Edge-aligned PWM signals are produced by the module

when the PWM time base is in the Free-Running or

Single-Shot mode. For edge-aligned PWM outputs, the

output has a period specified by the value in PTPER

and a duty cycle specified by the appropriate Duty Cycle

driven active at the beginning of the period (PTMR = 0)

and is driven inactive when the value in the Duty Cycle

If the value in a particular Duty Cycle register is zero,

then the output on the corresponding PWM pin will be

inactive for the entire PWM period. In addition, the out-

put on the PWM pin will be active for the entire PWM

period if the value in the Duty Cycle register is greater

than the value held in the PTPER register.

FIGURE 15-2:

EDGE-ALIGNED PWM

15.4

Center-Aligned PWM

Center-aligned PWM signals are produced by the

module when the PWM time base is configured in a

Continuous Up/Down Count mode, as shown in

Figure 15-3.

The PWM compare output is driven to the active state

when the value of the Duty Cycle register matches the

value of PTMR and the PWM time base is counting

downwards (PTDIR = 1). The PWM compare output is

driven to the inactive state when the PWM time base is

counting upwards (PTDIR = 0) and the value in the

PTMR register matches the duty cycle value.

If the value in a particular Duty Cycle register is zero,

then the output on the corresponding PWM pin will be

inactive for the entire PWM period. In addition, the out-

put on the PWM pin will be active for the entire PWM

period if the value in the Duty Cycle register is equal to

the value held in the PTPER register.

FIGURE 15-3:

CENTER-ALIGNED PWM

15.5

PWM Duty Cycle Comparison

Units

There are three 16-bit Special Function Registers

(PDC1, PDC2 and PDC3) used to specify duty cycle

values for the PWM module.

The value in each Duty Cycle register determines the

amount of time that the PWM output is in the active

state. The Duty Cycle registers are 16 bits wide. The

LSb of a Duty Cycle register determines whether the

PWM edge occurs in the beginning. Thus, the PWM

resolution is effectively doubled.

15.5.1

DUTY CYCLE REGISTER BUFFERS

The three PWM Duty Cycle registers are double-

buffered to allow glitchless updates of the PWM

outputs. For each duty cycle, there is a Duty Cycle reg-

ister that is accessible by the user and a second Duty

Cycle register that holds the actual compare value

used in the present PWM period.

For edge-aligned PWM output, a new duty cycle value

will be updated whenever a match with the PTPER

duty cycle buffers are automatically loaded into the

Duty Cycle registers when the PWM time base is

disabled (PTEN = 0) and the UDIS bit is cleared in

PWMCON2.

When the PWM time base is in the Continuous Up/

Down Count mode, new duty cycle values are updated

when the value of the PTMR register is zero and the

PWM time base begins to count upwards. The contents

of the duty cycle buffers are automatically loaded into

the Duty Cycle registers when the PWM time base is

disabled (PTEN = 0).

Period

Duty Cycle

PTPER

PTMR

Value

New Duty Cycle Latched

PTPER

PTMR

Value

Period

Period/2

Duty

Cycle

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