DSPIC30F6010A_11 Datasheet, PDF (99/236 Pages) Microchip Technology – High-Performance, 16-bit Digital Signal Controllers

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.
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
register.
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
register is matched. The timer will begin counting
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.
© 2011 Microchip Technology Inc.
DS70150E-page 99