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ADS1220: Support for daisy-chained SPI

Alan Gillespie71
Prodigy 50 points

Part Number: ADS1220
Other Parts Discussed in Thread: RM44L520,

Hi,

I'm using 3 identical ASD1220 circuits in my application with a RM44L520 MCU.

I need to sample all 3 ADCs simulataneously, however the MCU only has 2 MibSPI modules. I am wondering if the ADS1220 could support daisy-chained MibSPI so that the combined data stream could be read into memory via a single MibSPI without processor overhead?

If this is not possible, would daisy-chaining work on the standard SPI module?

As an alternative, if I used 2 MibSPI plus the standard SPI (with transactions initiated by CS falling edge on SPI) - would this work?

Many thanks for you feedback or suggestions in advance,

- Alan

  • 0
    TI__Mastermind 30408 points

    Alan,

    1. The ADS1220 does not support daisy-chain mode. We have other devices that do as well as simultaneous sampling devices if you would like to consider alternatives.
    2. You should be able to do what you want using the three SPI ports. In order to do this, you will need to make sure that a common 4.096MHz external conversion clock is connected to each device.  Using the internal conversion clock will have tolerance in the total conversion time, which will allow some devices to finish converting before others.  Using a common external conversion clock will have better tolerance than the internal conversion clock, so that the conversion time for each device is the same.  Thus, you can read the three devices shortly after the busy signals drop and get a simultaneous conversion.
    3. You could use continuous conversion mode, and read data after all three Data Ready signals drop. This would require one start START/SYNC before the first read then reading back based on Data Ready.  Alternatively, you could use Single-Shot conversion mode which would require a START/SYNC before each read.

    I hope this helps clarify your options.

    Art

  • 0 in reply to Art Kay
    Prodigy 50 points

    Good evening Art,

    Thank you for providing a prompt and detailed response to my query.

    Best wishes,

    - Alan