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Strange Random Spikes

Zubair Lutfullah
Intellectual 295 points
Other Parts Discussed in Thread: ADS1298

Hello everyone.

Our Setup -> ARM, Linux, SPI, Level Translators as ADS1298 in on 3.3V, ARM on 1.8V.

We acquire 40,000 samples of data from the ADS at an SPI clock set via linux to be 24MHz.

After acquiring the raw-data, we plot it using MATLAB. Wrote a small function for data handling.

RDATA mode. i.e. One transfer of 28 bytes.

TX : First byte RDATA. Rest bytes 0x00.

RX : Ignore First Byte. Rest Bytes data.

4KSPS Configuration.

Sometimes. A sample or two would be corrupted without any reason that we can come up with.

One out of 40000 samples spikes.

I remember using RDATAC Mode once and seeing a lot of these spikes. But they wouldnt come in RDATA mode.

Is there something basic we are missing?

Awaiting guidance from the Oracles

:)

Zubair

Test signal. The line in the bottom is the status register.

Also. I've noticed. That not all leads are like that. A couple of leads spike. Rest are ok. Visible if you zoooom in.

  • TI__Guru**** 181521 points

    Hi Zubair,

    Are you able to trigger on one of these spikes and capture what is going on with the SPI communication lines at the time of the spike?  My first inclination would be that the communication is corrupted in some way.  Can you tell us how you control the /CS input as well?

  • in reply to Tom Hendrick
    Intellectual 295 points

    Hello

    Triggering on one of these. I don't think so. Its sort of a static acquisition script. We play with the data offline after converting it then.

    I could provide you a file containing the raw binary stream if you want? Even have a function in Matlab to read it.

    I had a hunch it was SPI as well. Reduced the speed to 16Mhz. Spike is still there.

    CS is grounded. And start pin high all the time. (Or was it low? The one which enables acquisition via opcodes only)

    Basic script->

    Reset ADS via Opcode

    Configure for 4KSPS.

    ADS_Start

    Acquisition (40,000 samples) . DRDY is captured via an interrupt handler in linux.

    ADS_Stop

    Thanks

    Zubair