DSPIC30F0010AT-30ESLASHS datasheet(97/236 Pages) MICROCHIP

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DS70150C-page 95

dsPIC30F6010A/6015

15.1

PWM Time Base

The PWM time base is provided by a 15-bit timer with

a prescaler and postscaler. The time base is accessible

via the PTMR SFR. PTMR<15> is a read-only Status

bit, PTDIR, that indicates the present count direction of

the PWM time base. If PTDIR is cleared, PTMR is

counting upwards. If PTDIR is set, PTMR is counting

downwards. The PWM time base is configured via the

PTCON SFR. The time base is enabled/disabled by

setting/clearing the PTEN bit in the PTCON SFR.

PTMR is not cleared when the PTEN bit is cleared in

software.

The PTPER SFR sets the counting period for PTMR.

The user must write a 15-bit value to PTPER<14:0>.

When the value in PTMR<14:0> matches the value in

PTPER<14:0>, the time base will either reset to ‘0’, or

reverse the count direction on the next occurring clock

cycle. The action taken depends on the operating

mode of the time base.

The PWM time base can be configured for four different

modes of operation:

• Free-Running mode

• Single-Shot mode

• Continuous Up/Down Count mode

• Continuous Up/Down Count mode with interrupts

for double updates

These four modes are selected by the PTMOD<1:0>

bits in the PTCON SFR. The Up/Down Counting modes

support center-aligned PWM generation. The Single-

Shot mode allows the PWM module to support pulse

control of certain Electronically Commutative Motors

(ECMs).

The interrupt signals generated by the PWM time base

depend on the mode selection bits (PTMOD<1:0>) and

the postscaler bits (PTOPS<3:0>) in the PTCON SFR.

15.1.1

FREE-RUNNING MODE

In the Free-Running mode, the PWM time base counts

upwards until the value in the Time Base Period regis-

ter (PTPER) is matched. The PTMR register is reset on

the following input clock edge and the time base will

continue to count upwards as long as the PTEN bit

remains set.

When the PWM time base is in the Free-Running mode

(PTMOD<1:0> = 00), an interrupt event is generated

each time a match with the PTPER register occurs and

the PTMR register is reset to zero. The postscaler

selection bits may be used in this mode of the timer to

reduce the frequency of the interrupt events.

15.1.2

SINGLE-SHOT MODE

In the Single-Shot Counting mode, the PWM time base

begins counting upwards when the PTEN bit is set.

When the value in the PTMR register matches the

PTPER register, the PTMR register will be reset on the

following input clock edge and the PTEN bit will be

cleared by the hardware to halt the time base.

When the PWM time base is in the Single-Shot mode

(PTMOD<1:0> = 01), an interrupt event is generated

when a match with the PTPER register occurs, the

PTMR register is reset to zero on the following input

clock edge, and the PTEN bit is cleared. The postscaler

selection bits have no effect in this mode of the timer.

15.1.3

CONTINUOUS UP/DOWN

COUNTING MODES

In the Continuous Up/Down Counting modes, the PWM

time base counts upwards until the value in the PTPER

downwards on the following input clock edge. The

PTDIR bit in the PTMR SFR is read-only and indicates

the counting direction The PTDIR bit is set when the

timer counts downwards.

In the Up/Down Counting mode (PTMOD<1:0> = 10),

an interrupt event is generated each time the value of

the PTMR register becomes zero and the PWM time

base begins to count upwards. The postscaler selec-

tion bits may be used in this mode of the timer to reduce

the frequency of the interrupt events.

Note:

If the Period register is set to 0x0000, the

timer will stop counting, and the interrupt

and the special event trigger will not be

generated, even if the special event value

is also 0x0000. The module will not update

the Period register, if it is already at

0x0000; therefore, the user must disable

the module in order to update the Period

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