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Section 18 Multi-Function Timer Pulse Unit (MTU)
Rev. 4.00 Sep. 14, 2005 Page 604 of 982
REJ09B0023-0400
Complementary PWM Mode PWM Output Generation Method: In complementary PWM
mode, 3-phase output is performed of PWM waveforms with a non-overlap time between the
positive and negative phases. This non-overlap time is called the dead time.
A PWM waveform is generated by output of the output level selected in the timer output control
register in the event of a compare-match between a counter and data register. While TCNTS is
counting, data register and temporary register values are simultaneously compared to create
consecutive PWM pulses from 0 to 100%. The relative timing of on and off compare-match
occurrence may vary, but the compare-match that turns off each phase takes precedence to secure
the dead time and ensure that the positive phase and negative phase on times do not overlap.
Figures 18.40 to 18.42 show examples of waveform generation in complementary PWM mode.
The positive phase/negative phase off timing is generated by a compare-match with the solid-line
counter, and the on timing by a compare-match with the dotted-line counter operating with a delay
of the dead time behind the solid-line counter. In the T1 period, compare-match a that turns off the
negative phase has the highest priority, and compare-matches occurring prior to a are ignored. In
the T2 period, compare-match c that turns off the positive phase has the highest priority, and
compare-matches occurring prior to c are ignored.
In normal cases, compare-matches occur in the order a → b → c → d (or c → d → a' → b'), as
shown in figure 18.40.
If compare-matches deviate from the a → b → c → d order, since the time for which the negative
phase is off is less than twice the dead time, the figure shows the positive phase is not being turned
on. If compare-matches deviate from the c → d → a' → b' order, since the time for which the
positive phase is off is less than twice the dead time, the figure shows the negative phase is not
being turned on.
If compare-match c occurs first following compare-match a, as shown in figure 18.41, compare-
match b is ignored, and the negative phase is turned off by compare-match d. This is because
turning off of the positive phase has priority due to the occurrence of compare-match c (positive
phase off timing) before compare-match b (positive phase on timing) (consequently, the waveform
does not change since the positive phase goes from off to off).
Similarly, in the example in figure 18.42, compare-match a' with the new data in the temporary
register occurs before compare-match c, but other compare-matches occurring up to c, which turns
off the positive phase, are ignored. As a result, the positive phase is not turned on.
Thus, in complementary PWM mode, compare-matches at turn-off timings take precedence, and
turn-on timing compare-matches that occur before a turn-off timing compare-match are ignored.