DocID025944 Rev 1

9/17

AN4445

A set of peripherals tailored for low power

16

that provides the needed functionalities and performance, while minimizing the power

consumption.

•

The low power universal asynchronous receiver transmitter (LPUART) is an UART

which allows bidirectional UART communications with a limited power consumption.

Only 32.768 kHz LSE clock is required to allow UART communications up to 9600

baud/s. Higher baud rates can be reached when the LPUART is clocked by clock

sources different from the LSE clock. Even when the microcontroller is in deep stop

mode , the LPUART can wait for an incoming UART frame while having an extremely

low energy consumption. The LPUART includes all necessary hardware support to

make asynchronous serial communications possible with minimum power

consumption).

•

The I2C is able to wakeup the MCU from Stop mode (APB clock is off), when it is

addressed. All addressing modes are supported. The HSI16 oscillator must be

selected as the clock source for I2CCLK in order to allow wakeup from STOP. During

Stop mode, the HSI16 is switched off. When a START is detected, the I2C interface

switches the HSI16 on, and stretches SCL low until HSI16 is woken up. HSI16 is then

used for the address reception. In case of an address match, the I2C stretches SCL

low during MCU wakeup time. The stretch is released when ADDR flag is cleared by

software, and the transfer goes on normally. If the address does not match, the HSI16

is switched off again and the MCU is not woken up.

•

The USART is able to wakeup the MCU from Stop mode when USART clock is HSI16

or LSE. Several sources of wakeup from STOP mode can be selected:

–

Wakeup on adress match

–

Wakeup on Start bit detection

–

Wakeup on RXNE.

Table 2. Functionalities depending on working mode (from Run/active to standby)

IPs

Run/Active

Sleep

Low-

power

run

Low-

power

sleep

Stop

Standby

Wakeup

capability

Wakeup

capability

CPU

Y

-

Y

-

----

Flash memory

Y

Y

Y

N

----

RAM

Y

Y

Y

Y

Y

---

Backup

registers

Y

Y

Y

Y

Y-Y-

EEPROM

Y

-

Y

Y

Y

-

-

-

Brown-out rest

(BOR)

Y

Y

Y

Y

YYY

-

DMA

Y

Y

Y

Y

----

Programmable

Voltage

Detector (PVD)

Y

Y

Y

Y

YYY

-

Power On

Reset (POR)

Y

Y

Y

Y

YYY

-