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I2C arbitration

Discussion in 'Electronic Design' started by [email protected], Apr 29, 2005.

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  1. Guest

    Hi all,

    In my system there are 3 MCU's sitting on the same I2C bus.
    Let us take a scenario where all the 3 MCU's issue a start condition
    at the same time and all the 3 MCU's issue the same slave address and
    R/W='1' of all the 3 MCU's.Now MCU1 wants to transmit 01010101 to the
    slave, while MCU 2 wants to transmit 01100110 to the slave and MCU3
    wants to transmit 01001111.Since it is a wired AND MCU2 loses the
    arbitration , my question is who will win the bus b/w MCU1 and MCU3
    becuase both of them transmit a zero at the same time the 3rd bit.

    Thanks in advance.

    ~Praveen
     
  2. Keith

    Keith Guest

    MCU 3 wins during the 4th bit.

    MCU1 01010101
    MCU2 01100110
    MCU3 01001111

    -Keith
     
  3. Bob Monsen

    Bob Monsen Guest

    Everybody continues until they notice that they have released SDA, but
    it's still being held down by somebody else. Thus, MCU3 wins.
     
  4. Pooh Bear

    Pooh Bear Guest

    How can you assure that they *all* issue a start condition
    *simultaneously* ?

    If you could do that - then you can avoid arbitration issues. QED !


    Graham
     
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