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ADS131E08: Daisy Chain Data Sequence and Period

Shota Mago
Expert 8110 points
Part Number: ADS131E08

Hi team,

I'm an FAE supporting some industrial customers in Japan.

My customer employs ADS131E08 for ECG monitoring and provided some questions as below.

  1. When using ADS131E08 2pcs and the data rate is 8ksps, will all Daisy Chain data transaction be completed every within 125us(1/8s)?
    (How long will it take for Daisy Chain transaction with above condition?)
  2. Could you please explain in detail Daisy Chain data transaction sequence with 2pcs, 8ksps, 24bit, 8ch?
    For example, D/S Fig.56 shows Daisy Chain data word but I'm not sure which channel's data will be sent at first.
    What will occur at xx span?
    What happens when sending channel 2 data after sending data on channel 1(Or nothing happen, just send data continuously)?
  3. Does fmod remain fixed frequency regardless of any other setting?

I'm looking forward to hearing back from you.

Best regards,

Shota Mago

  • 0
    TI__Guru 66186 points

    Hello Shota-san,

    Thank you for your post.

    1. For daisy-chained devices to operate properly, the channels from all devices in the chain must be synchronized. This means that you must use the same clock source. One option is to output the internal oscillator from Device 0 and connect it to the CLK pin of Device 1. Please review the clock options listed in Table 4.

    If the channels are synchronized correctly, then all 16 channels will output a new conversion result at the same time every 125 us. You must read 2 x (STATUS + 8 * 24 bit data) + 1 "don't care" bit = 433 bits before the devices complete their next conversion. Use this number when calculating the minimum required SCLK frequency as explained in 9.5.2.2 of the datasheet.

    2. One SPI transaction will look like this:

    [(Device 0: STATUS + CH1 + CH2 + ... + CH8) + "don't care" bit + (Device 1: STATUS + CH1 + CH2 + ... + CH8)]

    3. Yes, fMOD is always equal to fCLK / 2.


    Best Regards,

  • 0 in reply to Ryan Andrews
    TI__Expert 8110 points
    Hi Ryan-san,

    It's been a long time since we met before!
    I rotated T&M under Taras-san when I was in Dallas, and currently working in Japan.
    Do you remember me?

    Thanks for your detail explanation and that exactly what I want.
    When I get any other questions from the customer, I will let you know again.

    Best regards,
    Shota Mago
  • 0 in reply to Shota Mago
    TI__Guru 66186 points
    Hi Shota-san,

    Yes - I remember you. Hope everything is going well!

    Let me know when you have an update from your customer.

    Regards,