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STM32L151xC STM32L152xC
Functional overview
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3.5 Low-power
real-time
clock and backup registers
The real-time clock (RTC) is an independent BCD timer/counter. Dedicated registers contain
the sub-second, second, minute, hour (12/24 hour), week day, date, month, year, in BCD
(binary-coded decimal) format. Correction for 28, 29 (leap year), 30, and 31 day of the
month are made automatically. The RTC provides two programmable alarms and
programmable periodic interrupts with wakeup from Stop and Standby modes.
The programmable wakeup time ranges from 120 µs to 36 hours.
The RTC can be calibrated with an external 512 Hz output, and a digital compensation
circuit helps reduce drift due to crystal deviation.
The RTC can also be automatically corrected with a 50/60Hz stable powerline.
The RTC calendar can be updated on the fly down to sub second precision, which enables
network system synchronization.
A time stamp can record an external event occurrence, and generates an interrupt.
There are thirty-two 32-bit backup registers provided to store 128 bytes of user application
data. They are cleared in case of tamper detection.
Three pins can be used to detect tamper events. A change on one of these pins can reset
backup register and generate an interrupt. To prevent false tamper event, like ESD event,
these three tamper inputs can be digitally filtered.
3.6 GPIOs
(general-purpose inputs/outputs)
Each of the GPIO pins can be configured by software as output (push-pull or open-drain), as
input (with or without pull-up or pull-down) or as peripheral alternate function. Most of the
GPIO pins are shared with digital or analog alternate functions, and can be individually
remapped using dedicated AFIO registers. All GPIOs are high current capable. The
alternate function configuration of I/Os can be locked if needed following a specific
sequence in order to avoid spurious writing to the I/O registers. The I/O controller is
connected to the AHB with a toggling speed of up to 16 MHz.
External interrupt/event controller (EXTI)
The external interrupt/event controller consists of 24 edge detector lines used to generate
interrupt/event requests. Each line can be individually configured to select the trigger event
(rising edge, falling edge, both) and can be masked independently. A pending register
maintains the status of the interrupt requests. The EXTI can detect an external line with a
pulse width shorter than the Internal APB2 clock period. Up to 83 GPIOs can be connected
to the 16 external interrupt lines. The 8 other lines are connected to RTC, PVD, USB,
comparator events or capacitive sensing acquisition.
