Underflow Output Action - Silicon Laboratories EFR32xG14 Wireless Gecko Reference Manual

21.3.4 Underflow Output Action

For each of the repeat registers, an underflow output action can be set. The configured output action is performed every time the coun-
ter underflows while the respective repeat register is nonzero. In PWM mode, the output is similarly only changed on COMP1 match if
the repeat register is nonzero. As an example, the timer will perform 7 output actions if LETIMERn_REP0 is set to 7 when starting the
timer in one-shot mode and leaving it untouched.
The output actions can be set by configuring UFOA0 and UFOA1 in LETIMERn_CTRL. UFOA0 defines the action on output 0, and is
connected to LETIMERn_REP0, while UFOA1 defines the action on output 1 and is connected to LETIMERn_REP1. The possible ac-
tions are defined in Table 21.2 LETIMER Underflow Output Actions on page
UF0A0/UF0A1
0b00
0b01
0b10
0b11
Note:
For the Pulse and PWM modes, the outputs will return to their idle states regardless of the state of the corresponding LETIMERn_REPx
registers. They will only be set active if the LETIMERn_REPx registers are nonzero however.
Note:
For free-running mode, LETIMERn_REP0 != 0 for output generation to be enabled.
The polarity of the outputs can be set individually by configuring OPOL0 and OPOL1 in LETIMERn_CTRL. When these are cleared,
their respective outputs have a low idle value and a high active value. When they are set, the idle value is high, and the active value is
low.
When using the toggle action, the outputs can be driven to their idle values by setting their respective CTO0/CTO1 command bits in
LETIMERn_CTRL. This can be used to put the output in a well-defined state before beginning to generate toggle output, which may be
important in some applications. The command bit can also be used while the timer is running.
Some simple waveforms generated with the different output modes are shown in
page 723. For the example, REPMODE in LETIMERn_CTRL has been cleared, COMP0TOP also in LETIMERn_CTRL has been set
and LETIMERn_COMP0 has been written to 3. As seen in the figure, LETIMERn_COMP0 now decides the length of the signal periods.
For the toggle mode, the period of the output signal is 2(LETIMERn_COMP0 + 1), and for the pulse modes, the periods of the output
signals are LETIMERn_COMP0+1. Note that the pulse outputs are delayed by one period relative to the toggle output. The pulses
come at the end of their periods.
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Table 21.2. LETIMER Underflow Output Actions
Mode
Idle
Toggle
Pulse
PWM
LETIMER - Low Energy Timer
722.
Description
The output is held at its idle value
The output is toggled on LETIMERn_CNT
underflow if LEIMERn_REPx is nonzero
The output is held active for one clock cy-
cle on LETIMERn_CNT underflow if LETI-
MERn_REPx is nonzero. It then returns to
its idle value
The output is set idle on LETIMERn_CNT
underflow and active on compare match
with LETIMERn_COMP1 if LETI-
MERn_REPx is nonzero.
Figure 21.8 LETIMER Simple Waveforms Output on
Reference Manual
Rev. 1.1 | 722