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Master to master in multi-master mode

Bernard PERRIN
Prodigy 160 points


I have 2 MSP430 connected to each other via I2C. Is it possible to exchange messages between them when they are both masters in multi-master mode?

I suspect that multi-master is used to arbitrate a concurrent access from 2 masters to a slave but not for the exchange of data between masters.

I have an interrupt line from the second MSP to the first one. So it would be possible to use the second MSP as a slave an the first as a master.

Which alternative is simpler?

  • 2 masters in multi-master mode (if the answer is yes to my first question)
  • A master-slave and an interrupt line

Thanks in advance for any kind of help.

  • 0
    Guru 318760 points

    In the I²C protocol, the master sends the device address, and the slave receives the device address, so it is not possible for two masters (or two slaves) to communicate with each other.

    You could either

    • use some separate mechanism to send a signal (like an interrupt line), or
    • let a device be listening in slave mode when it's idle, and switch to master mode only when it wants to send something.
  • 0 in reply to Clemens Ladisch
    Prodigy 160 points
    Thank you Clemens for your clear answer. I use now an interrupt line and the listening device then turns in master mode when the other one flip to slave. It works well in both direction.

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