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LMH0397: LMH0397 SPI addressing

brian moore48
Prodigy 100 points
Part Number: LMH0397

SPI bus addressing: If several devices are in a SPI daisy chain, how do you access each device individually? For example, if you want each device in the chain to be configured individually, or if you want to access only one device but not the others? I do not see any means to set the address via pins as is the case with SMB.

  • 0
    TI__Expert 4695 points

    Hi Brian,

    Hope you're doing well. To answer your question:

    Each device on the SPI Bus is connected to the Master/Controller device by a CS (Chip Select: active low) line. When the chip select is low for a device, that device becomes the active device and can begin a data transaction with the Master/Controller. The CS for the non-active devices will be high.

    Please review this video from TI precision labs for more specific information on SPI interface www.ti.com/.../6245520669001. Please be aware that there are many different naming conventions, but that the operation of SPI is the same regardless.

    Best,

    Nick P.

  • 0 in reply to Nick Peabody
    Prodigy 100 points

    Nick, the video did not tell me anything I don't already know. What I want to know is, using the daisy chain SPI connections, is it possible to program each LMH0397 device in the chain with a different configuration? I assume if there were 4 devices in the chain, this would use a 68 bit word, with each 17 bit portion containing the config for the corresponding device in the chain that it ends up in when the SSN is deasserted? Yes or no? We need to know as we are laying out a PCB and want to know if this is possible using daisy chain.

  • 0 in reply to brian moore48
    TI__Expert 4695 points

    Hi Brian,

    To answer your question, your assumption is correct and the LMH0397 is capable of daisy chaining. 

    A consideration to make is that data overflows from one peripheral to the next so the first piece of data you transmit will end up in the last peripheral.

    Do you have any other considerations for your PCB and daisy chaining you want to bring up?

    Best Regards,

    Nick