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Simple multi-channel serial ADC (8-ch)?

Discussion in 'Electronic Design' started by Joerg, Feb 15, 2007.

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  1. linnix

    linnix Guest

    If they use an open standard interface like Jtag, then it would be
    possible. We tried with AVR, but the Jtag interface is not totally
    open.
    It's hard to do that. We need to work on both sides at the same
    time. For example, we are now trying to figure out the data transfer
    protocol, and we need to program both Window and Linux.

    The gdb protocol for reading is:

    $ m <addr> , <count> # <checksum>
    $ m <addr> , <data> # <checksum>
    with + (ACK) and - (NAK)

    We would need protocol extensions to write to buffer,
    then a write flash command.
    But they all use web servers, and many of them are Linux. As long as
    they don't have to touch them, it would be fine. Think of it as a
    Jtag programming server.

    We don't want the client to mess with the Linux box as all. All the
    user interfaces will be done on the Window side. The Linux box will
    be running on read-only 64M Flash Drive. There is no user interface
    to it, except for an RJ-45 for network and a USB cable for programming
    the target.
    No problem, you will need a uC eventually, for another project.
     
  2. Joerg

    Joerg Guest

    Never used one of those. In my lab I had two Viewsonic but they went to
    the recycler because their job had been taken over by PCs. One thing I
    must say is that those terminals had tens of thousands of hours on them
    yet never let me down.
     
  3. Joerg

    Joerg Guest

    AFAICT they don't, and actually migrated a bit away from JTAG with the
    new F2xxx family. The old ones can usually be bootloaded quite well.
    If that box is really small it would work.
    Yep, and one is coming. That one must have a uC because it'll have to
    transmit data via wireless.
     
  4. linnix

    linnix Guest

    Tell that to the Honeywell Engineers who are recalling their products
    built with flash based uC. Show me how to convince my customer who
    would never consider "flash" permanent.
     
  5. linnix

    linnix Guest

    My target is a lunch box (in size), but there is no reason why you
    can't use a PDA or cell phone (with usb). There are cell phones
    running on Linux and internet connected.
     
  6. Joerg

    Joerg Guest

    Stand-alone ADC boards can be made quite versatile. It's all
    controllable via registers and stuff. That can also be done with a uC
    but the issues that tend to creep up there is noise from the uC itself.
    On acquisition boards with uC we usually needed several iterations to
    optimize sleep modes etc. Not required with a plain ADC board because
    it's quiet the microsecond the SPI clock stops. But you are right, if
    there was a hard bug it would be a re-design.
     
  7. Hi Jörg,
    You should look in NGs and Web around and ask by the sourgeforge folks. And
    of course look the appnotes from TI. The salesmen often don't know the tools
    in backstage. They know the Features they want to sell...
    Wondering !?! A few years ago, long before the f2xxx was released, they
    marks exact this feature: a propper brown-out circuit in their MSP430F1xy
    and f4xy
    go to the next university hang a sheet of paper out there with a promise of
    a few dollars and you will get this job done very quickly.
    may be you can deliver teh clock for µC this way external, without the usage
    from internal fll.

    Marte
     
  8. Joerg

    Joerg Guest

    It wasn't the sales folks whom I asked :)
    I know, some of them do. But a lot of them don't and I never really
    understood why not.

    Sure. But this time I was able to do without ;-)
    With a fully static design that works. The only thing you have to pay
    attention to, usually, is the AD converter in there. Some concepts go
    haywire if you take the clock away in the middle of the game. IIRC some
    16bit SD converters then need three "dummy conversions" before you get a
    good one.
     
  9. Joerg

    Joerg Guest

    Was it caused by flash memory loss? If so, please let us know which uC
    that was if you are at liberty to tell. Might avoid some black eyes.
     
  10. Hi Jörg,
    Even cracks don't know all these very special things.
    Sure, you have allways to know what you do ;-) Several SD needs more than 3
    Cycles to get valid results. SD converters are designed to convert streams
    not single samples. Therefore they usually don't have a S&H or such things
    and more often they have included filters...

    Marte
     
  11. linnix

    linnix Guest

    Flash is just my guess.
    It was in the news for recalling a few hundred AT91SAM7S256. I
    sometimes have strange results with AVR flash as well. I don't know
    if they are built with the same process, or if it's just a certain
    batch.
     
  12. Guest

    So you have customers that reject any flash based designs?
     

  13. The ADM3 was a very early glass teletype. One of the first in the
    "Low cost" category. They were built to last a lifetime. I think I
    still have a complete unit, but I scrapped a lot of them for the nice LV
    power transformers.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  14. Joerg

    Joerg Guest

    Well, suppose there was such a routine (which AFAIK there isn't) and the
    top notch guys at a company would not know about a tool with so much
    marketing power. Then it would be time for a huge organizational
    structuring effort. Because it would mean that there is a company that
    doesn't know where its assets are. I doubt that's the case with TI.
    Which is why, I guess, parts like the MSP430F2013 wouldn't cut it in
    this application.
     
  15. linnix

    linnix Guest

    No, they insist on being able to reprogram it in the field (at the
    very least), as well as remotely probing the flash for
    verifications. A local Window station monitors the remote targets'
    flash and data memories,
    that part of it is working fine. We are currently working on remotely
    programming an ARM Cortex M3 using remote gdb server on the targets.

    We are still trying to figure out the best way to do it. One solution
    is to create a virtual flash port on the gdb server. Namely, a block
    of registers interpreted by the gdb server and jtag into flash. For
    example, Flash Address Register (FAR), Flash Data Register (FDR),
    Flash Control Register (FCR) and Flash Status Register (FSR). They
    should be a reserved block not used by ARM and/or vendors (LMI, TI and
    ST are prospective vendors).

    We already have the ability to access real or virtual registers, as
    well as sram. In response to the FCR, the gdb server jtag/swd a small
    program on sram to rewrite the flash.

    By the way, a single monitor station could track/maintain several
    remote stations miles away. Actual sample rates (both system and apps
    data) are very low (HZs), so it could be done with GSM/GPRS as well.
    Of course, the targets are firewalled to talk to authorized IPs only.

    Actually, this discussion should really be in comp.arch.embedded
     
  16. Joerg

    Joerg Guest

    FWIW, while browsing around for some other parts I found the Analog
    Devices AD7928. An 8-ch ADC that also comes in 10-bit and 8-bit flavors
    and has a reasonable street price. Both the config string and required
    HW handshake look quite clean. Nice part.
     
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