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What error will occur on transmitting using asynchronous serial I/O?

Latest Updated:03/01/2005

Question:

(Serial Interface)  When transmitting using asynchronous serial I/O, if erroneous data (c) is received between correct data (a) and (b) due to noise, what kind of error will occur? And how can I counter this? [2005/03/01]

Answer:

  1. When "data (b) receive" is started while "data (c) receive" is in progress:
    • Bit displacement will occur in data (b) receive.
  2. When data-receive completion is confirmed after "data (c) receive" is completed
    but before "data (b) receive" starts:
    • Since the receive buffer full flag is set to "1" by the completion of "data (c) receive",
      this is recognised as data-receive completion and erroneous data (c) is read.
  3. When data-receive completion is confirmed after both data (c) and data (b) receives are completed:
    • An overrun error occurs due to both data (c) and (b) being received.

[Countermeasures]
For 1 and 3
"Receive reset" to clear state by switching serial I/O and data receive from "disabled" to "enabled". Specifically, reset the receive shift register, receive buffer register and all status flags including error flags. When erroneous data is received due to noise or another error occurs due the receipt of erroneous data, etc., subsequent data will not be received correctly, so the receive operation must be reset using the above process.
For 2
Check the read data in the program.

(#104806)

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