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SMBus

Karlson Greene
Prodigy 20 points
Other Parts Discussed in Thread: TCA9548A, TCA9517

Does anyone know how many slaves an MSP430 Master can interface with on an SMBus?  I am interested in interfacing up to 64 devices but not sure if this is possible.

  • 0
    TI__Genius 16510 points

    Hello Karlson,

    I am moving this post to the MSP430 forum since your question pertains specificially to the MSP430's implementation about I2C.

    Typically, the SMBus protocol is quite similar to the standard I2C, and you should not have any issues interfacing to a SMBus interface.

  • 0
    TI__Genius 16510 points
    I Misread your post, my mistake. I thought you were asking if you could use MSP430 with SMBus.

    The SMBus/I2C interface has a limitation of 400 pF at standard speed and fast mode (100 kHz and 400 kHz).

    A good rule of thumb (worst case estimation) is to assume 10 pF per slave device, and don't forget your board cap, so 50 slaves will likely violate your max capacitance.

    There are ways around this, with buffers that split the capacitive load such as TCA9517, but you must also make sure all slaves have unique I2C/SMBus addresses. No 2 slaves are allowed to have the same address, or you will have communication issues. In this case, devices such as an I2C switch (TCA9548A) will allow you turn on/off portions of the bus to select certain portions of your bus.