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P82B96: I2C between two boards

Marada Naveen Kumar
Intellectual 615 points
Part Number: P82B96

Hi

I am trying to implement I2C communication b/w two boards containing F28335 MCUs in Master-slave mode.Every thing works fine when both are powered up.

whenever the slave is powered down,the Master is sensing bus busy and the voltage levels on the bus is changing from 3.3(Vcc) to 1.5V. I believe the issue is due to the common supply & ground and pull ups on the slave side are changing the voltage levels.when the slave is again powered up,i need to reset the I2C module through the software in Master for comm to happen. I've tried to eliminate this by placing diodes in the pull up paths at slave end,but still the issue repeats. Please suggest how to eliminate this ,Is there any alternative or other circuit config to communicate b/w two boards?.

The slave is supposed to be powered by the same supply of master,but can be powered off independently.Also i would like to make multi-master communication between more than 3 nodes on different boards connected on a mother board.Does the use of I2C Buffers such as P82B96 will help?

Thanks in advance,

Naveen M.

  • 0
    TI__Mastermind 23406 points

    Hello Naveen,

    Do you have a schematic of your design?  It sounds like a buffer could help you isolate the I2C lines, but I am trying to understand what you are seeing and why before I make recommendations. 

    -Francis Houde

  • 0 in reply to fhoude
    Intellectual 615 points

    Hi Francis,

    I cant give you the exact design schematic.But it looks like this

    where the slaves are also MCUs and are configured for multi master communication. And each node has VDD generated from a regulator which has other loads such as I/O ports of MCU,supplies for other auxiliary ICs and ofcourse ground is common for all nodes.

    So if there are only two nodes on the bus,whenever one node is powered down ,as i said the other node is sensing bus busy and the voltage levels are dropping around 1.5V. If there are three nodes on the bus and one node is powered down,communication is happening b/w remaining two nodes but the logic high level on the bus is not proper(not VDD)..I believe this is happening because of the connection of pull ups to VDD on each node and common ground is acting as a resistive divider on VDD in the powered down node.

    My intention is to completely isolate the powered down node from the bus.

    Regards,

    Naveen M