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TMS320F28027: Networking multiple 28027 thro I2C

Lenin Prakash
Intellectual 660 points

Part Number: TMS320F28027

Hi

  In one of our application, we have to forma network of multiple MCU's . Is I2C would be the preferred communication protocol

to form this network. In this one of the MCU will act as a master and all others will be slave. The MCU's will be in multiple PCB's. (though all the PCB's will be stacked nearby)

Is there any limitation on the number of slaves and the length of the network.

Thanks

Lenin.

  • 0
    TI__Mastermind 45606 points
    Hi Lenin,

    Yes, there is a limitation to the number of slaves. It's limiting factor is the address length, 7-bit addressing (typically used) supports 127 slave devices and 10-bit supports 1023 slave devices.

    There are limitations to I2C signal lengths as well, you can find a lot of material about this topic online. I2C is meant to have short wired communication, preferably between ICs on the same PCB. In your case you'll want to be cautious of the bus capacitance and resistance on the signal lines. I2C Standard and Fast mode are spec'd at a 400pF max bus capacitance.

    What clock speed are you planning on having? Typically the slower your comms, the longer the signal length can be.

    Best,
    Kevin
  • 0 in reply to Kevin Allen18
    Intellectual 660 points

    Hi Kevin

      Thanks for the response.  We will be using maximum of 10 slave MCU's and the maximum length of the network might not increase 50 cm.

    The clock frequency we are planning to have 100 kHz (corresponding to 100 Kbps). In fact it's ok for us to even further reduce this speed..

    But i just looked at that manual where it is mentioned two possible speeds ( 100 Kbps or 400 Kbps)..

      Is it possible to further reduce the speed ?

    Also is the length of 50 Cm is ok ?

    Thanks

    Lenin.

  • 0 in reply to Lenin Prakash
    TI__Mastermind 45606 points

    Hi Lenin,

    The two speeds represent I2C standard (100KHz) and fast (400KHz) modes, but you don't have to run at these exact speeds. Our device meets the fast mode spec, so you can clock the I2C bus up to 400KHz.

    See the I2C Clock Generation section, 10.1.4, of the TRM for information on how to configure the clock speed:

    http://www.ti.com/lit/sprui09

    Is that 50 cm of just PCB traces? or a combination of wires & PCB traces? The kind of cable / wiring you use is important for long communication lengths. I'm no expert on I2C cable types / lengths, but I'd be a little cautious with 10 devices being on the bus, as it will increase capacitance. I'd highly recommend doing some research of the topic online.

    There are also I2C bus extender ICs out there for enabling operation over further lengths. More of an FYI, probably won't be useful for your network. See this TI one if interested:

    Hope this helps,

    Kevin

  • 0 in reply to Kevin Allen18
    Intellectual 660 points

    Hi Kevin

       Thanks for the clarification on the I2c clock speed. The length I mentioned is inclusive of traces and cable length.

    I will check Bus extender IC and get back for any further support.

    Thanks

    Lenin.