• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 46 subscribers
  • Views 181 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1298: 5 cascaded devices problem

AL_Spain
Intellectual 340 points
Part Number: ADS1298

Hi all, and thanks in advance.

We have our electronic design with 5 cascaded ADS1298 devices. Our design have multiple switches to configure the number of ADS1298 devices working at the same time, and it is possible to connect and disconnect the entire ADS1298 conversor like a modular design. The main processor is the Teensy 4.0 development board (according to our evaluation, there is no problem with SPI bit rate and so on). Although there is no difference between conversors when connected in cascade, in our case we identify them as first conversor (with reference electrodes), second, third, fourth and fifth conversors.

Our design works fine with 4 cascaded ADS1298 devices, but when we try to connect the fifth conversor, our design does not work. We have tested many different things:

  1. According to the power supply of each ADS1298 conversor: we have checked it and all of them are fine. We use a USB connector (connected to a PC) to power the entire electronics (main processor and 5 conversors).
  2. Our impression is that there is any problem related with SPI bus and the number of ADS1298 devices. Why? Because we have checked the next items:
    1. Before starting to acquire data with any ADS1298, we configure some registers from each conversor (ADS1298), and check them from firmware. When 4 conversor modules are connected, the registers configuration (from each conversor) are fine, and also the data acquisition. When 5 conversor modules are connected, at least the register writting command fails in all conversors, because there are no changes on register values.
    2. When we configure our "electronic system" with two ADS1298 connected (the first and the fifth conversor modules) in cascade, the system works fine (register writting commands and data acquisition). In this configuration only conversor modules number 1 and number 5 are connected in the electronic design.
    3. But when we connect all 5 conversor modules (with firmware configured to acquire data only from conversor modules 1 and 5), it does not work (register writting commands fails).  

SPI connections are as follows:

  • DOUT (SPI_OUT) pins, from each ADS1298 conversor, can be connected (or disconnected via switch) to the same MISO pin on the processor (Teensy 4.0).
  • DIN (SPI_IN) pins, from each ADS1298 conversor, are directly connected to the same MOSI pin on the processor (Teensy 4.0).
  • CS (chip select) pins, from each ADS1298 conversor, can be connected (or disconnected via switch) to different GPIOs on the processor.
  • SCLK is common to all conversors and the processor.
  • START pin is common to all conversors.
  • CLK is also common to all conversors.

Our first impression is something related with impedance, or electronic characteristic...

Do you know why it does not work? Do you have any suggestion?...

Thanks a lot.

Best regards

  • 0
    TI__Genius 11550 points

    Hi Andres,

    Thanks for the post. Please see my comment below.

    1. Is it possible to verify the design with an external power supply instead of using the USB power supply?

    2. The digital SPI connections for the cascade configuration look fine. I would recommend probing the SPI bus with a logic analyzer/oscilloscope to help identify the issues when all 5 cascaded modules are connected. This FAQ on the SPI debug may help.

    Thanks

    -TC

  • 0 in reply to TCT
    Intellectual 340 points

    Hi TC,

    Thanks for your suggestions.

    1. I think there is no possibility to use an external power supply. We use the USB connection not only for powering the devices, but also to acquire data (serial COM connection with PC).
    2. Thanks for the suggestion with oscilloscope, we will try it.

    Thanks a lot.

    Andres.