RM0453 Rev 1 959/1461
RM0453 Low-power timer (LPTIM)
981
28.4.7 Trigger multiplexer
The LPTIM counter may be started either by software or after the detection of an active
edge on one of the 8 trigger inputs.
TRIGEN[1:0] is used to determine the LPTIM trigger source:
• When TRIGEN[1:0] equals ‘00’, The LPTIM counter is started as soon as one of the
CNTSTRT or the SNGSTRT bits is set by software. The three remaining possible
values for the TRIGEN[1:0] are used to configure the active edge used by the trigger
inputs. The LPTIM counter starts as soon as an active edge is detected.
• When TRIGEN[1:0] is different than ‘00’, TRIGSEL[2:0] is used to select which of the 8
trigger inputs is used to start the counter.
The external triggers are considered asynchronous signals for the LPTIM. So after a trigger
detection, a two-counter-clock period latency is needed before the timer starts running due
to the synchronization.
If a new trigger event occurs when the timer is already started it is ignored (unless timeout
function is enabled).
Note: The timer must be enabled before setting the SNGSTRT/CNTSTRT bits. Any write on these
bits when the timer is disabled is discarded by hardware.
28.4.8 Operating mode
The LPTIM features two operating modes:
• The Continuous mode: the timer is free running, the timer is started from a trigger event
and never stops until the timer is disabled
• One-shot mode: the timer is started from a trigger event and stops when an LPTIM
update event is generated.
One-shot mode
To enable the one-shot counting, the SNGSTRT bit must be set.
A new trigger event re-starts the timer. Any trigger event occurring after the counter starts
and before the next LPTIM update event, is discarded.
In case an external trigger is selected, each external trigger event arriving after the
SNGSTRT bit is set, and after the repetition counter has stopped (after the update event),
and if the repetition register content is different from zero, the repetition counter gets
reloaded with the value already contained by the repetition register and a new one-shot
counting cycle is started as shown in Figure 263.
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