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Original question:

ADS8558: Daisy Chain

ADS8558: ADS8558

Bob Foley
Prodigy 10 points
Part Number: ADS8558

Hello,

I have the exact same setup as the OP (Connie,) and I don't feel that the answer given was sufficient. There are 96 clock cycles in the SPI transaction - only 32 of which are needed for the SDI to each chip. She asked "Where does the 32 bits for the control register fit into the 96 clock transfer?". Figure 2 on page 15 of the datasheet only shows a 32-bit transaction.

Currently, I am just repeating the 32-bit Control Register value 3x for the 96-bit transaction, but that doesn't appear to work. I need to do a RESET between conversion attempts in order to get it to work, which is obviously less than ideal.

Any thoughts?

Thanks.

-Bob

  • 0
    TI__Mastermind 24970 points

    Bob,

     Since incoming information to ADS8558 is not daisy chained, you need to communicate to each device's SDI to configure it.  thus if you have three devices, you will also have 3 SDI lines, to each device.  Then these devices can share one SDO line.

    The timing for SDI is shown in Figure 2 page 15 in the datasheet shows one frame of communication. 

    Repeating the same command through one SDI line is not going to do anything, it will simply configure the first device. 

    Regards

    Cynthia