Parity Modes


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Thread: Parity Modes

  1. #1
    Join Date
    Aug 2005
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    Default Parity Modes

    I need to output different parity modes using one pic i.e. 9600 8N1 9600 8E1 9600 8O1 from my understanding of the PBP manual I can only choose between even, odd or none using the define command. Im still new to all this serial stuff so I would appreciate if someone could confirm this for me.
    Thanks Sphere.

  2. #2
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    Default

    Hi Sphere,

    If I understand correctly, you want to change parity modes at Run-Time?

    If so, then you are correct. Using either HSEROUT or SEROUT2 you can only change them at Compile-Time.

    If you generate your own parity, and manipulate the registers manually, you can use the USART in 9-bit mode to get the 8E1 and 8O1, and turn off 9-bit mode for 8N1.

    DT

  3. #3
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    Default How

    Thanks for the reply, you where correct about changing parity modes at Run-Time? but still being relativity green around the ears regarding pbp how do I do this.

    Thanks Sphere.

  4. #4
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    Default

    Well, first let's look at how the parity works.

    It's calulated by counting the number of 1's in the byte. For instance the letter "J" which is 01001010, 3 bits are a 1.

    If using EVEN parity, the parity bit will be set to 0, since 3 is not an even number. ODD parity would be 1, if used.

    For the letter "K" 01001011, 4 bits are a 1. So EVEN parity = 1, ODD = 0.

    As for sending that via the USART ...
    First, set up SPBRG, TXSTA and RCSTA like normal. (many other posts here show how to do that)

    Set TXSTA.6 (TX9) to 1.   Selects 9-bit transmission
    The parity bit goes in TXSTA.0 (TX9D)   9th bit of Transmit Data
    Then put the byte to be sent in TXREG
    and away she goes.
    DT

  5. #5
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    Aug 2005
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    Default Thanks

    Ill give it a go over the weekend.
    Thanks again Sphere.

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