Reverse polarity in Direct serial data


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  1. #1
    Join Date
    Nov 2003
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    Default Reverse polarity in Direct serial data

    I was struggling to get it right with direct serial data (no rs232 drivers etc).

    One PIC, a 16F1827, was set to transmit RS-232 serial at TTL level and the bit 4 of BAUDCTL was set for this. The output drives a ASK little transmitter with appropriate data to keep the DC level somewhere in the middle, so the receiver's data slicer can extract the data.

    The other PIC, a 16F886 was set to receive the data from the ASK receiver module and I was naive enough to trust that bit 4 of the famous BAUDCTL register was enough to get the job done.

    Three days to discover the little detail in the data sheet, that this little bit 4 inverts ONLY the data to be transmitted and NOT the incoming to RX pin.

    True, datasheet states that little phrase "transmit inverted data to RB7/TXCK pin" but was too careless to spot really see it. A simple inverter like a transistor or opamp will do the job but was happy to believe a bit 4 can save few parts here.

    Hope this helps others on this pitfall.

    Ioannis

  2. #2

    Default Re: Reverse polarity in Direct serial data

    If you have the pins available you could run the RX through the comparator to invert it.

  3. #3
    Join Date
    Nov 2003
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    Posts
    2,991

    Default Re: Reverse polarity in Direct serial data

    Never thought of that! Very good idea. A little bit of rearranging might do it.

    Thanks!

    Ioannis

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