Low Power Real-Time Clock And Backup Registers; Gpios (General-Purpose Inputs/Outputs) - STMicroelectronics STM32L151CB Manual

Functional overview
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 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 a programmable alarm and programmable periodic
interrupts with wakeup from Stop and Standby modes.
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The programmable wakeup time ranges from 120 µs to 36 hours
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Stop mode consumption with LSI and Auto-wakeup: 1.2 µA (at 1.8 V) and 1.4 µA (at
3.0 V)
●
Stop mode consumption with LSE, calendar and Auto-wakeup: 1.3 µA (at 1.8V), 1.6 µA
(at 3.0 V)
The RTC can be calibrated with an external 512 Hz output, and a digital compensation
circuit helps reduce drift due to crystal deviation.
There are twenty 32-bit backup registers provided to store 80 bytes of user application data.
They are cleared in case of tamper detection.
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 23 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.
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STM32L151xx, STM32L152xx