DocID13284 Rev 2 229/564
UM0404 The general purpose timer units
The reload mode triggered by T3OTL can be used in a number of different configurations.
Depending on the selected active transition the following functions can be performed:
• If both a positive and a negative transition of T3OTL is selected to trigger a reload, the
core timer will be reloaded with the contents of the auxiliary timer each time it overflows
or underflows. This is the standard reload mode (reload on overflow/underflow).
• If either a positive or a negative transition of T3OTL is selected to trigger a reload, the
core timer will be reloaded with the contents of the auxiliary timer on every second
overflow or underflow.
• Using this “single-transition” mode for both auxiliary timers allows to perform very
flexible pulse width modulation (PWM). One of the auxiliary timers is programmed to
reload the core timer on a positive transition of T3OTL, the other is programmed for a
reload on a negative transition of T3OTL. With this combination the core timer is
alternately reloaded from the two auxiliary timers.
Figure 87 shows an example for the generation of a PWM signal using the alternate reload
mechanism.
T2 defines the high time of the PWM signal (reloaded on positive transitions) and T4 defines
the low time of the PWM signal (reloaded on negative transitions).
The PWM signal can be output on T3OUT with T3OE = ‘1’, P3.3 = ‘1’ and DP3.3 = ‘1’. With
this method the high and low time of the PWM signal can be varied in a wide range.
Note: The output toggle latch T3OTL is software accessible and may be changed, if required, to
modify the PWM signal. However, this will NOT trigger the reload of T3.
Avoid selecting the same reload trigger event for both auxiliary timers as both reload
registers will try to load the core timer at the same time. If this happens, T2 is disregarded
and the contents of T4 is reloaded.
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