RM0367 Rev 7 617/1043
RM0367 Low-power timer (LPTIM)
635
24.4.2 LPTIM trigger mapping
The LPTIM external trigger connections are detailed hereafter:
24.4.3 LPTIM reset and clocks
The LPTIM can be clocked using several clock sources. It can be clocked using an internal
clock signal which can be any configurable internal clock source selectable through the
RCC (see RCC section for more details). Also, the LPTIM can be clocked using an external
clock signal injected on its external Input1. When clocked with an external clock source, the
LPTIM may run in one of these two possible configurations:
• The first configuration is when the LPTIM is clocked by an external signal but in the
same time an internal clock signal is provided to the LPTIM from configurable internal
clock source (see RCC section).
• The second configuration is when the LPTIM is solely clocked by an external clock
source through its external Input1. This configuration is the one used to realize Timeout
function or Pulse counter function when all the embedded oscillators are turned off
after entering a low-power mode.
Programming the CKSEL and COUNTMODE bits allows controlling whether the LPTIM will
use an external clock source or an internal one.
When configured to use an external clock source, the CKPOL bits are used to select the
external clock signal active edge. If both edges are configured to be active ones, an internal
clock signal should also be provided (first configuration). In this case, the internal clock
signal frequency should be at least four times higher than the external clock signal
frequency.
24.4.4 Glitch filter
The LPTIM inputs, either external (mapped to GPIOs) or internal (mapped on the chip-level
to other embedded peripherals), are protected with digital filters that prevent any glitches
and noise perturbations to propagate inside the LPTIM. This is in order to prevent spurious
counts or triggers.
Before activating the digital filters, an internal clock source should first be provided to the
LPTIM. This is necessary to guarantee the proper operation of the filters.
Table 108. LPTIM1 external trigger connection
TRIGSEL External trigger
lptim_ext_trig0 PB6 or PC3
lptim_ext_trig1 RTC alarm A
lptim_ext_trig2 RTC alarm B
lptim_ext_trig3 RTC_TAMP1 input detection
lptim_ext_trig4 RTC_TAMP2 input detection
lptim_ext_trig5 RTC_TAMP3 input detection
lptim_ext_trig6 COMP1_OUT
lptim_ext_trig7 COMP2_OUT
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