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ADS8361 mode IV with DMA

Alberto Biancalana
Intellectual 380 points
Other Parts Discussed in Thread: ADS8361
Hi, I'm planning to use ADS8361 for a 4 channel FSK-FH decoder, using 6418EVM, 5-6k interface board andADS8361EVM.
I want to use mode IV operation of ADS8361, and have the 4 channels 16 bit samples written by DMA on a memory page in interleaved fashion, being sure to associate channels and memory locations.

I read the full documentation of 8631 and also the application note for C6711 (which should be good also for 6418), where MCBSp is configured to receive 20 bit frames with 2 byte delay and a single 16 bit word, but I don't understand a basic thing.

How can I start ADS8361 operations getting samples starting from the first of the 4 channels? and stop operations at any time and then restart again getting samples starting from the first channel?

Should I drive M0 low, generate one or some CONVST/RD pulses with MBsp, stop sending pulses, then drive M0 high, initialize DMA and start MCBsp running?. And do all this after I've stopped and I need to start again?
M0 can't be driven by the EVM using ADS8361 EVM, so should I wire to some GPIO to do this?
Or I should do some other way?
Sorry for the long question, I was not able to explain with less details.
Any help is really appreciated.
Alberto
  • 0
    TI__Guru**** 172886 points

    Hi Alberto,

    This sounds like a very interesting project to use the ADS8361 with!  One thing that is not made very clear in the ADS8361 data sheet is that the device starts off from power up in Mode 1.  There is another application note here http://www.ti.com/lit/an/slaa167/slaa167.pdf which you might find helpful.  That document was written for the F2000 series DSP's but it goes into more detail and includes a few scope shots that may help you realize a method to get your project running.

    Figure 4 in the application note mentioned above shows how you can drive M0 low via GPIO and force the ADS8361 into a synchronized state that allows you to simply read the 16-bit conversion results and store the data by CHA0, CHB0, CHA1, CHB1...  The alternative to this is to take all 18-bits from the ADS8361 SDOA (2 CH ID bits + 16-data bits) and sort the data based on the status of the channel ID bits; 00 is A0, 01 is B0, 10 is A1 and 11 is B1.  See Figure 13 in the ADS8361 data sheet for details and note that the first sample should be discarded (this is Mode 1 from power-up).

  • 0 in reply to Tom Hendrick
    Intellectual 380 points

    Thanks Tom, the F2000 document gives much more infos.  I'll find a way to bring a GPIO signal of 6414EVM to the 8361EVM to drive M0 as required.

    Can I ask about a last doubt on 8361?
    This is probably a stupid question that you already answered in your post, but I'm a careful guy since I have very short time to setup this work.
    All the characteristics of 8631 are ok for my 4 channel FSK modem utilization, like sampling rate, resolution, aperture, noise and so on.
    Anyway, I see that in the 8361 datasheet the only suggested application are motor control and others, all of which are out of my knowledge, but not data acquisition or communications.  I think that those are simply suggested applications, also due to the simultaneous sampling feature, but there can be any parameter or reason that escapes me for which 8361 could non fit applications different by the suggested ones, like the one I need?
    Thanks and best regards
    Alberto
  • 0 in reply to Alberto Biancalana
    TI__Guru**** 172886 points

    Hi Alberto,

    My apologies for the slow response here - the ADS8361 was designed for use with applications that require simultaneous sampling.  The thought was customers who are trying to measure two phase currents, or the output of a sinusoidal encoder in a motor control application would find the interface 'easy' to use while incorporating the ability to capture two distinct signals at the same time.  That being said, there is absolutely nothing about the part that makes it specific exclusive to a motor control application.  Anywhere you need a multi-channel, high speed, high resolution ADC, the ADS8361 would definitely be an appropriate solution.

  • 0
    Intellectual 380 points

    Absolutely no problem for the time, Tom,  and thanks again you for your support.

    I just submitted the project concept based on ADS8361, 5-6K Interface Board, and 6418EVM, and now is coming time of develop SW to test the system.

    Thanks so much

    Alberto