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What's an ADC Sequencer? and what does it do ?

Islam Elnady
Intellectual 340 points
Other Parts Discussed in Thread: TM4C123GH6PM

Hi,
I'm using TM4c123GH6PM to acquire analog value from a potentiometer. I found some initialization setup for one sequencer out of four, but didn't get in exactly what its job is.. 

  • 0
    TI__Guru**** 244400 points
    Hello Islam,

    Did you read the TM4C123GH6PM data sheet section on Sample Sequencers (13.3.1 Sample Sequencers)? If yes, then what do you make of it, let us discuss that first.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Intellectual 340 points
    Hello Amit,
    Yes I did .. I just want to understand how ADC works in the launchpad,, and for the the sequencer part, I didn't understand its task very well.. all I got is that a sequencer holds samples from multiple input sources.. would you just explain it a little please ?
  • 0 in reply to Islam Elnady
    TI__Guru**** 244400 points
    Hello Islam

    It does not hold samples from multiple input sources. It has the list of input sources that need to be sampled on a trigger. It is on the trigger condition being true, does the sampler interacts with the Analog Front End, and stores the results from the "sequenced" sources.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Intellectual 340 points

    Hello Amit,
    How many input channels a single sequencer can interact with?
    and also for an ADC module? and in case that ADC module acts on multiple inputs, does that affect on the max allowed sampling rate ?

  • 0 in reply to Islam Elnady
    TI__Guru**** 244400 points
    Hello Islam,

    This is mentioned in the ADC Chapter of the Datasheet. I would ask you to first read the data sheet and viz-a-viz have a query/question, I would be glad to answer further

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Intellectual 340 points
    Hi Amit,
    I'm sorry but this is not mentioned in the data sheet. I have read all of the ADC part. Would you please tell me where exactly I can find it in the data sheet?

    Thanks,
    Islam
  • 0 in reply to Islam Elnady
    TI__Guru**** 244400 points
    Hello Islam,

    Then wouldn't that be required to formulate the right set of questions and would it not help you an others that data sheet is not clear and we can then be discussing on the forum to resolve the inconsistencies if any in the data sheet.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 47900 points

    Hi Amit,

    By firm's/my read - very much of poster's curiosity is well satisfied by the MCU manual.   Having past written such manuals - this "sample sequencer" detailing does appear "reasonable."   (yet - like many things - always could be made better...)    I attach (one) key portion of the manual for review:

  • 0 in reply to cb1
    TI__Guru**** 244400 points
    Hello Islam,

    Apologies for my over insistence on reading the data sheet. cb1- has proved that the details were insufficient (and thank you for that).

    The Sequencer is a like a sequential task list which schedules A/D conversions. Each entry requires property like, channel number, differential or single ended input, interrupt generation and end of sequence. The trigger (hardware or processor initiated) starts the execution of a sequencer and the entry corresponding to end of sequence stops the sequencer. At the end of it the sequencer FIFO contains the entry for the A/D converted value in the order of the A/D channels programmed in the sequencer MUX register.

    Regards
    Amit
  • 0 in reply to cb1
    Intellectual 340 points

    Hi cb1,
    I have read this part and couldn't find it very promising. But thank you for the help.

  • 0 in reply to Amit Ashara
    Intellectual 340 points
    Hi Amit,
    Thanks for the details. I still have questions about the effect on sampling rate due to utilizing of multiple inputs, which is not mentioned in the "data sheet" ...

    Regards
    Islam
  • 0 in reply to Islam Elnady
    TI__Guru**** 244400 points
    Hello Islam,

    And what are those questions?

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 47900 points

    Hi Amit & Islam,

    May I take (one) shot at Islam's question?   If Sample Sequencer 0 is chosen (8 step sequences) it is possible for those 8 steps to address:

    • just one channel (repeated 8 times)
    • a mix of channels - with some channels repeated
    • eight different channels

    Amit must verify - but our experience reveals that in (any) of those 3 cases - the ADC conversion rate remains constant.   That said - if just a single channel is placed w/in that "8 step sequence" the conversion rate of that channel is maximized.   (highest possible conversion rate [but for special conditions])   In contrast - if 8 different channels were chosen - the, "Individual Channel Conversion Rate" is one-eighth of that described earlier.  

    This leads to your acceptance that "Conversion Rate" may not be - in fact often will not be - realized across multiple (different) channels.

    Recall that these MCUs usually employ more than one ADC module - and that there are methods (via that 2nd ADC module) to double your effective conversion rate.

    It would appear that "Conversion Rate" - by itself - requires stronger definition.   The MCU's spec targets the back to back (successive) conversion rate - and (to my mind) does not descend into individual channel conversion rates.   (i.e. when multiple channels are enabled & placed w/in the sample sequence.)

  • 0 in reply to cb1
    TI__Guru**** 244400 points
    Hello cb1,

    The max conversion rate is 1MSPS for TM4C123x devices when not using the Phase shift feature between 2 ADC controllers. What you are describing is the Effective Channel Conversion Rate and you are spot on the interpretations on the 3 cases.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 47900 points

    Hi Amit,

    Thank you - your notation, "Effective Channel Conversion Rate" does seem "tighter" than my, "Individual Channel Conversion Rate."    I "am troubled" by the use of a relatively "open word" (effective).

    Might it be that an "Amit-cb1 hybrid" ... "Effective, Individual Channel Conversion Rate" combines the best of both worlds?

  • 0 in reply to cb1
    TI__Guru**** 244400 points
    Hello cb1

    Makes for an acronym EICCR (as a regulatory body).

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 47900 points

    Let that (new) regulatory body meet upon alternate, "ground hog days" when sun is high and snow fills the field.   I'll supply the starched wigs (one clearly worn by one favored candidate - currently) if you'll supply the long, black robes. (required by such an august body...)