Specifications

PWM Waveform Generation With Compare Units and PWM Circuits
6-57 Event Manager (EV)
6.6.3 Asymmetric PWM Waveform Generation
The edge-triggered or asymmetric PWM signal is characterized by modulated
pulses which are not centered with respect to the PWM period, as shown in
Figure 6–22. The width of each pulse can only be changed from one side of
the pulse.
Figure 6–22. Asymmetric PWM Waveform Generation With Compare Unit and PWM Circuits
(x = 1, 3, or 5)
Timer
(PWM)
period 1
Timer
(PWM)
period 1
Dead band
Timer value
PWM
x
(active high)
PWM
x+1
(active low)
Compare value
greater than
period
Compare matches
To generate an Asymmetric PWM signal, GP timer 1 is put in the continuous
up-counting mode and its period register is loaded with a value corresponding
to the desired PWM carrier period. The COMCONx is configured to enable the
compare operation, set the selected output pins to be PWM outputs, and en-
able the outputs. If dead-band is enabled, the value corresponding to the re-
quired dead-band time should be written by software into the DBT(3:0) bits in
DBTCONx(11:8). This is the period for the 4-bit dead-band timers. One dead-
band value is used for all PWM output channels.
By proper configuration of ACTRx with software, a normal PWM signal can be
generated on one output associated with a compare unit while the other is held
low (or off) or high (or on), at the beginning, middle, or end of a PWM period.
Such software controlled flexibility of PWM outputs is particularly useful in
switched reluctance motor control applications.