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I have a question regarding the UART Transmit module. What are the ways to detect if the UART Transmit buffer has completed the byte transfer?

Rohan Lele
Intellectual 260 points

Among the ways to detect the completion of UART Transmit, the UART transmit interrupt flag is one.

Is the Transmit interrupt flag (UCTXIFG) set even when the transmit interrupt is disabled? Is the flag automatically cleared or do we need to clear it in software?

.

Second way to detect the completion of UART Transmit is Transmit Ready Interrupt Flag (UCTXRDYIFG). What is the difference between UCTXRDYIFG and UCTXCPTIFG ?

Third way to detect the completion is to poll the UCBUSY flag. 

Which one of these three methods is the best to continuously send out characters on the TX line?

  • 0
    Guru 23000 points

    On the product page of your MCU, you can download a User's Guide, these answers (most of) your questions.

    But anyhow;

    Rohan Lele said:
    Is the Transmit interrupt flag (UCTXIFG) set even when the transmit interrupt is disabled?

    yes

    Rohan Lele said:
    Is the flag automatically cleared or do we need to clear it in software?

    automatic

    Rohan Lele said:
    What is the difference between UCTXRDYIFG and UCTXCPTIFG ?

    No, this is probably an error in the documentation or a yet to be described difference in the buffers.

    Rohan Lele said:
    Which one of these three methods is the best to continuously send out characters on the TX line?

    UCTXIFG

    The difference is;

    UCTXIFG indicates that a new byte in the transmit buffer can be written, but a previous byte may be pending.

    UCTXCPTIFG indicates that the byte is sent, possibly including STOP and the Tx buffer is empty.

    UCBUSY = 0 indicates that the (e)USCI(_A) is fully ready, everything is received and nothing more to send.

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