AN4635 datasheet(7/34 Pages) STMICROELECTRONICS

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AN4635

Summary of features

The LPUART has less features compared to the USART, however it is able to operate using

less power and using the LSE clock more efficiently.

The main features for the two peripherals are summarized in Table 2.

The USART is also able to operate using LSE clock, the communication speed is limited to

4000 baud in case of oversampling by 8, 2000 baud when oversampling is by 16.

When using the LPUART, only the 32.768 kHz LSE clock is required to allow UART

communications up to 9600 baud with minimal energy consumption and very precise speed

setting allowed by the external crystal.

For higher speeds (for example the 57600 baud used for BT LE) the LPUART energy

efficiency advantage drops, but still remains measurable around 5% (see Section 6.9:

Higher communication speed).

This document focuses on communication at 9600 baud, common to many applications: the

efficiency advantage of LPUART is more pronounced when using wakeup from Stop at the

9600 baud speed setting.

Table 2. Comparison of features

Configuration

LPUART

USART

LSE 9600 baud option

Synchronous mode

IrDA SIR ENDEC block

Smartcard mode

Auto baud rate detection

Modbus communication

LIN mode

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