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Thread: UART/serial BREAK questions

  1. #1

    Default UART/serial BREAK questions

    I know the break signal is basically asserting the line for longer than a frame would normally be thus introducing a bad frame technically. I read something about 2 frames + 3 more stop bits or something about the length. Probably breaks are not even used all that often these days, but my question is this:

    If one issues a break - is this like a reset in a way for the line/device? Should the break be fit into an existing stream of transmitted bytes, or would a break generally clear the tx buffer if there are characters remaining to be sent? What about the RX side? Should the RX buffer be flushed as well if a device sends a break?

  2. #2
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    Check the UART datasheet for the device that you're using, but AFAIK, it does not clear the buffer. But why would you send a break when there are already characters to be sent all queued up?

  3. #3

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    I agree, I don't see the point, but I am wondering how breaks usually worked. If a terminal sends a break, are there other things it does along with that such as clear rx buffer, clear tx buffer, clear handshaking status, etc.

  4. #4
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    Looking at the datasheets for the 8251A and the 2661, on receive, BREAK seems to be just a special receive condition, like a framing error. Doesn't really affect anything else and continues on its merry way at the completion of the break.

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