I2C arbitration

Apr 29, 2005 3 Replies

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praveen.kantharajapura 21 years ago

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

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Keith 21 years ago

MCU 3 wins during the 4th bit.

MCU1 01010101 MCU2 01100110 MCU3 01001111

-Keith

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Bob Monsen 21 years ago

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

Regards, Bob Monsen

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Pooh Bear 21 years ago

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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