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Write
PWM START
Configure
PWM
Trigger event
PWM output
Interrupt
Write
PWM START
P1D
PER+1
Ignored events
2.3.2
Continuous Operation
Peripheral Architecture
The PWM is stopped from the event-triggered one-shot mode operation by changing the MODE bit to 0
(disable). When the PWM is disabled, the output is immediately driven to the configured inactive state.
Figure 3. PWM Event-Triggered One-Shot Mode Operation (P1OUT = 1, INACTOUT = 0, EVTRIG = 1,
PWM_RPT = 1)
In continuous mode operation, the PWM produces the repeating output waveforms continuously without
stopping. For continuous mode operation, the PWM should first be configured for mode, period, and
first-phase duration, along with other configuration options. The PWM uses the last programmed set of
parameters once it is started by writing a 1 to the START bit in the PWM start register (START). Unlike the
one-shot mode, the repeat count does not affect the continuous operation. To select continuous mode,
configure the MODE bit in the PWM configuration register (CFG) to 2h.
Once started, the PWM asserts/deasserts the output as configured, driving to first-phase output level
during the first phase and the opposite level during the second phase. Once a period expires, the next
period starts. When a period starts, the PWM copies the period and first-phase duration registers into a
set of internal shadow registers and maintains the counts there. An interrupt is also generated (if enabled)
after the registers are copied. This buffering scheme and interrupt timing allows the CPU or EDMA to
program the durations for the next period while the current period is running.
The PWM is stopped during the continuous mode operation by either disabling it or by reconfiguring it to
one-shot mode using the MODE bit. Whenever the PWM is disabled, the output is immediately driven to
the configured inactive state. To allow the PWM to stop gracefully from continuous operation, upon an
interrupt, configure the PWM to one-shot mode operation. The PWM then operates for RPT + 1 periods
and stops by itself (sending an interrupt, if enabled). Note that unlike normal one-shot mode operation,
another write to the START bit is not required for the one-shot mode operation to start.
While operating in continuous mode, the minimum period for the PWM is 8 cycles.
shows programming of period/first-phase-duration, and the resulting output waveform, and
interrupt signal for continuous operation.
SPRUEE7A – May 2006 – Revised September 2007
Pulse-Width Modulator (PWM) Peripheral
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