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ADS1291 daisy chain

Daniele Mereu73
Prodigy 30 points
Other Parts Discussed in Thread: ADS1291, ADS1298

Hi all

I need to design a board with 8 ADS1291 in daisy chain mode connected with a master cortex M3 microcontroller. Could you help me to understand how to connect them properly?

The goal is to connect them so that we can be sample 8 bipolar signals synchronously to the maximum sampling frequency of 1KHz.

My questions are:

  1. One of the eight ADS1291 must generate the clock for everyone else?
  2. Synchrony is given by the CLK signal and the START command?
  3. From the point of view of the SPI connection, given that in the daisy chain configuration uses only one chip select signal, the configuration commands are executed by the various slave only to the level transition of the chip select?
  4. How can I send different multi-byte configurations command at various ADS1291, without "disturbing" others, if I have only one chip select signal?

Thanks you at all

Daniele

  • 0
    TI__Mastermind 18285 points
    Daniele,

    I am moving your post to the correct forum.
  • 0
    TI__Mastermind 38745 points
    Hey Daniele,

    1. Correct, this will ensure the state machines and converters are running at exactly the same clock.
    2. Correct, if the devices are running on the same clock, the START signal or command will synchronize all of conversions such that DRDY will occur at the same time for all devices effectively achieving simultaneous sampling.
    3. If you look at figure 42 in the datasheet, you can see that separate CS pins can control devices separately such that the other communications can occur on the same bus.
    4. Refer to answer 3.

    If you are looking for an eight channel simultaneous sampling converter, I'd advise you take a look at the ADS1298, it will provide eight simultaneous sampling delta-sigma ADCs without the headache of daisy-chaining.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Prodigy 30 points

    Hi Brian and thank you for the answer.

    I know that exists the ADS1298 but I have the 8 single ADS1291 on 8 different little boards and, for minimize the number of connections (and also because the number of boards could vary), I need to use the daisy chain connection mode.

    For these reansos, I tried to ask for explanations on points 3 and 4.

    Could you help me to better understand please?

    Thank you very much!

    Daniele

  • 0 in reply to Daniele Mereu73
    TI__Mastermind 38745 points
    Hey Daniele,

    All of the devices may share the same SCLK, DIN, and DOUT pins, but each device should have its own unique CS. This way the master can chose which chip it is talking to individually as well as cycle through devices when it is collecting data. In addition, if you synchronize devices to the same clock and use the START pin or command to begin conversions simultaneously, you will only need to connect one of the device's DRDY pins since they will all finish converting at the same time.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Prodigy 30 points

    OK Brian, then you're saying me that I can't connect ADS1291 in daisy chain mode, like this image, with a single chip select?

    Excuse me, but for me it's very important to understand this point.

  • 0 in reply to Daniele Mereu73
    TI__Mastermind 38745 points
    Hey Daneile,

    That configuration would not work because when attempting to read a register or conversion data, MISO for the slaves would conflict. You must chose slave devices individually since when CS is high for a device, the DOUT pin for that device will be hi-z.

    Regards,
    Brian Pisani