Datasheet

DS10668 Rev 6 25/126
STM32L031x4/6 Functional overview
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3.6 Low-power real-time clock and backup registers
The real time clock (RTC) and the 5 backup registers are supplied in all modes including
standby mode. The backup registers are five 32-bit registers used to store 20 bytes of user
application data. They are not reset by a system reset, or when the device wakes up from
Standby mode.
The RTC is an independent BCD timer/counter. Its main features are the following:
• Calendar with subsecond, seconds, minutes, hours (12 or 24 format), week day, date,
month, year, in BCD (binary-coded decimal) format
• Automatically correction for 28, 29 (leap year), 30, and 31 day of the month
• Two programmable alarms with wake up from Stop and Standby mode capability
• Periodic wakeup from Stop and Standby with programmable resolution and period
• On-the-fly correction from 1 to 32767 RTC clock pulses. This can be used to
synchronize it with a master clock.
• Reference clock detection: a more precise second source clock (50 or 60 Hz) can be
used to enhance the calendar precision.
• Digital calibration circuit with 1 ppm resolution, to compensate for quartz crystal
inaccuracy
• 2 anti-tamper detection pins with programmable filter. The MCU can be woken up from
Stop and Standby modes on tamper event detection.
• Timestamp feature which can be used to save the calendar content. This function can
be triggered by an event on the timestamp pin, or by a tamper event. The MCU can be
woken up from Stop and Standby modes on timestamp event detection.
The RTC clock sources can be:
• A 32.768 kHz external crystal
• A resonator or oscillator
• The internal low-power RC oscillator (typical frequency of 37 kHz)
• The high-speed external clock
3.7 General-purpose inputs/outputs (GPIOs)
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 alternate function registers. All GPIOs are high current capable.
Each GPIO output, speed can be slowed (40 MHz, 10 MHz, 2 MHz, 400 kHz). 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 a dedicated
IO bus with a toggling speed of up to 32 MHz.
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