Analog Devices SHARC ADSP-214 Series Hardware Reference Manual page 384

Functional Description
Inserting additional emergency dead time into one of the PWM signals of
a given pair during these transitions is only needed if both PWM signals
would otherwise be required to toggle within a dead time of each other.
The additional emergency dead time delay is inserted into the PWM sig-
nal that is toggling into the on state. In effect, the turn on (if turning on
during this dead time region), of this signal is delayed by an amount of
2 × PWMDT × PCLK from the rising edge of the opposite output. After
this delay, the PWM signal is allowed to turn on, provided the desired
output is still scheduled to be in the on state after the emergency dead
time delay.
Figure 7-4 illustrates two examples of such transitions. In (a), when transi-
tioning from normal modulation to full on at the half cycle boundary in
double update mode, no special action is needed. However in (b), when
transitioning into full off at the same boundary, an additional emergency
dead time is necessary. This inserted dead time is a little different to the
normal dead time as it is impossible to move one of the switching events
back in time because this would move the event into the previous modula-
tion cycle. Therefore, the entire emergency dead time is inserted by
delaying the turn on of the appropriate signal by the full amount.
7-16
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ADSP-214xx SHARC Processor Hardware Reference