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CCS/TM4C123GH6PM: Launchpad+ Need for Speed (ADC)

James Carucci
Prodigy 170 points
Part Number: TM4C123GH6PM
Other Parts Discussed in Thread: TM4C1294NCPDT, ADS127L01,

Tool/software: Code Composer Studio

Sup Y'all

I'm using this launchpad for a mixed signal project. I'm running up against an issue where I really need high speeds and good resolution so I can measure activity in the 250kHz range. I'm considering marrying my launchpad with this MCP3911 (https://www.mouser.com/ds/2/268/20002286C-1150165.pdf) which goes up to ~4MHz but I'm not keen on writing my own SPI drivers for this. I'm wondering if anyone in the community has driver code for a fast external ADC ~+2MHz...

I figure since TI probably makes quite a few ADC's that'll meet that spec, this problem's probably solved already. If anyone could help me out I'd appreciate it greatly

Cheers,

Jim

  • 0
    TI__Guru 72500 points
    Hi Jim,
    I know a co-worker in the TI ADC group is working on something with the ADS127L01. His project is using a TM4C1294NCPDT, instead of the TM4C123GH6PM. It uses the SSI and uDMA. Might that be helpful?
  • 0 in reply to Bob Crosby
    Guru 117855 points

    (Note:  I quite carefully,  "Clicked upon "poster Jim C's post - somehow  this  "like-less" forum addresses Bob - not my intent...)

    Vendor here has a "reasonably" complete, (external) "ADC inventory/offering" - yet to be (even) "more pro" - you may visit "ADI's site" - especially since they "swallowed" Linear Tech.

    "Fishing" w/in a single stream - when "so many" (high-fish count ones) abound - may not insure the "Best & Fullest, Capture Experience."

  • 0
    Genius 3850 points
    you probably want to take a look at the errata, or talk to an experienced programmer of luminary parts first.

    speed-wise, the part can do 250ksps - but check the errata first.

    if you really want higher speed with onboard adc, check out LPC43xx. Or other vendors for that matter.

    if you want to go with outboard adc, do a little bit of math. at 4msps, assuming each sample takes at least 2 bytes, you are talking about spi clock of 64Mhz. That's beyond the capabilities of most experienced embedded programmers (and their layout teams), especially if you want to do it with wires dangling out of your launchpad.
  • 0 in reply to Danny F
    Guru 117855 points

    Your guidance as to the "forced limits" - imposed (especially) by vendor's (comparatively slow) SPI clock speed - to my mind - proves, "spot-on!"
    Note too - that we have each suggested a, "higher performing" MCU.    (mine - non LPC - via PM to friend/fellow NYC escapee - poster...)

  • 0 in reply to Bob Crosby
    Prodigy 170 points

    Bob,

    That's definitely something I'm interested in seeing as how I have that development board as well. Please keep in mind I'm relatively new to this fast and furious ADC business so a couple of questions:

    1. How fast has your colleague sampled at? I put 4MHz because I am an aggressive individual but I can definitely can away with between 1 and 2 MHz.

    2. What would it take for me to adapt the code to the TM4C123GH6PM?

    3. I am willing to trade resolution for speed. I only need about 10-12bits but I really want to be able to sample at least in the range mentioned in 1 above

    Thanks,

    Jim

  • 0 in reply to James Carucci
    Guru 117855 points

    James Carucci said:
    How fast has your colleague sampled?    I put 4MHz...

    Was not,  "poster Danny's" guidance more "fruitful" to your desire?          Danny provided the "General Solution Technique" - which (surely/always) trumps "colleague hearsay" - or the "too often" (singular/insular) methods -  "normally" offered up.

    It was noted that 4MHz (potential/theoretical) ADC results would demand a 64MHz SPI clock.     (far outside the reach of  TM4C)   

    By scaling ...  2Mhz would demand 32MHz - and your (further reduced) goal of 1MHz ... relaxes the SPI clock to 16MHz.

    Your review of the MCU's SPI specs  (far back in the MCU manual) reveals its max.  SPI Clock...     Yet again - both Danny & this reporter have suggested,  "a more capable (external ADC eliminating) MCU."