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Muscle Man
Muscle Man
Associate III
March 30, 2017
Question

What is the difference between HAL UART and HAL USART?

  • March 30, 2017
  • 2 replies
  • 4078 views
Posted on March 30, 2017 at 16:22

Hi to all!,

Having to write a simple UART device driver for my application (based on a STM32L073 mcu),

I noticed that HAL presents two kind of uart drivers: an HAL UART and an HAL USART.

Digging a little bit into the related HAL code, I would say that 

HAL USART are more suited to

use USART macrocell as a simple uart; instead HAL UART seems to be more useful when 

a need for LIN/Multimaster mode or IrDA arises. Am I right?

Thanks in advance to everyone would take me a feedback!

Scrat75.

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    2 replies

    S.Ma
    S.Ma
    Principal
    March 30, 2017
    Posted on March 30, 2017 at 17:49

    Actually it should be the opposite. With UART, you get RX/TX only. With USART superset, you also get RTS/CTS/CK signals, plus some additional serial protocols in there (Lin, sometime smart card interface with TX and CK pins, etc...)

    Guenael Cadier
    Guenael Cadier
    ST Employee
    March 31, 2017
    Posted on March 31, 2017 at 18:37

    Hi Stefano,

    My answer is different from previous one. Actually, HAL USART is dedicated to operation in Synchronous mode, I mean transfers are synchronized with SCLK signal (controlled by CPHA and CPOL).

    When transmitting => as soon as some data are to be transferred, SCLK will be output.

    When Receiving => as soon as SCLK is generated, some acquisition is done on RX line (no need for start bit for instance).

    Usart way of working is more close to a SPI master mode.

    HAL UART is related to asynchronous transfers (for example, reception is triggerred by detection of a start bit). HW flow control, LIN, ... are to be served using HAL_UART_xxx() APIs.

    For IRDA, a HAL_IRDA group is available.

    Now aside from available HAL services, your device embedds several UART/USART instances. In corresponding datasheet (

    http://www.st.com/content/ccc/resource/technical/document/datasheet/d8/b3/7b/dc/18/22/44/f5/DM00141036.pdf/files/DM00141036.pdf/jcr:content/translations/en.DM00141036.pdf

    ) you should be able to find capabilities of each USART instance available on your L073. Some features are available only on some instances :

    For example, you could use USART1/2/3/4 instance for achieving UART transfers (using HAL_UART functions), USART1/2/3/4 instance for achieving USART transfers (using HAL_USART functions), but if you want to use HAL_IRDA functions, you will have to use either USART1 or USART2 instance in the device (USART3 and 4 not supporting Irda). Please extracted table below.

    0690X00000606gMQAQ.png

    Hope this helps.

    Regards

    Guenael

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