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MSP430I2041: Recommend how to synchronize sampling across multiple 'i2041s

pathfinder
Genius 12790 points
Part Number: MSP430I2041
Other Parts Discussed in Thread: MSP430I2040

Support,

Is it possible and can you recommend how to hook up multiple MSP430i20xx's so the sampling is synchronized across all the devices?

Regards,

Marc

  • 0
    Guru 26200 points
    Hello,

    use one MCU as a master and many slaves connected to a line driven only by master.
    Change on this line should generate an interrupt on slaves.
    In this way slaves could be synchronized.
  • 0 in reply to Tomasz Kocon
    TI__Guru 56685 points
    Hello,

    As Tomasz pointed out, you would need to have some sort of signal that you send simultaneously to all of the MSP430I2041s. they are still not going to be perfectly in sync as each device will have their own jitter and DCO variation and thus slightly different response times.
  • 0 in reply to Jace H
    TI__Genius 12790 points
    Hello,
    Can you verify that an external TACLK can be used across multiple devices to supply the SD24s with clock?

    In the Users Guide, page 601, figure 26-1, it shows TACLK as one of the input clocks to the SD24 subsystem.

    Regards,
    Marc
  • 0 in reply to pathfinder
    TI__Guru 56685 points
    Hello Pathfinder,

    To clarify here, I think you are referencing the User guide for MSP430F5xx6xx devices (slau208). The MSP430i2040 series of devices have a different User Guide ( www.ti.com/.../slau335 ). From here you can see the SD24 clock is generated internally, but there is an option to feed the specific 16.384MHz system clock into the device.
  • 0 in reply to Jace H
    Guru 26200 points
    Hello Pathfinder,

    a clock signal distribution is a piece of engineering.
    Your initial question was about synchronized sampling across multiple 'i2041s.
    Without a technical requirements specification our information exchange would not bring you a solution.
  • 0 in reply to Tomasz Kocon
    TI__Genius 12790 points

    Tom,

    It really comes down to comparing an MSP430F6775x solution to what can be done with the i20xx.

    The technical requirements is to have SD24 sampling clock sync'd across multiple devices.  Today, the 6775x uses the TACLK input on each device supplied from a high precision clock distribution device.  It is not dependent on the device's main clock.  This guarantees common SD24 clock independent of any DCO jitter.

    The i20xx does not have TACLK as an option to supply the SD24 sample clock

    I think the answer is pretty clear at this point.  It cannot be done.  There seems to be no way to guarantee a common SD24 clock across multiple devices.

    Regards,

    Marc

  • 0 in reply to pathfinder
    Guru 26200 points
    Marc,
    agreed, I have misinterpreted you initial question, it was not about triggering but about syncing.
  • 0 in reply to Tomasz Kocon
    TI__Genius 12790 points
    Tomasz,

    Can a GPIO pin used as an interrupt be used to trigger the SD24? I have looked through data sheet/users guide and I see the ability to use GPIO as an interrupt but can't figure out if/where i can have the ISR trigger the SD24. Can you point me to the details?

    Regards,
    Marc
  • 0 in reply to pathfinder
    TI__Guru 56685 points
    Hey Marc,

    The SD24 module on the MSP430i2040 series doesn't have a trigger conversion feature like other MSp430 ADCs you may be more familiar with. You need to set the enable conversion bit in the appropriate channel specific SD24 register to start conversions. So could you use a GPIO interrupt to start the SD24 to sample? Yes, but not automatically. You would need to enable the appropriate bit within the GPIO ISR.
  • 0 in reply to Jace H
    TI__Genius 12790 points

    Jace,

    I think i'm following.  Here is what I'm thinking ...  ultimately, as before, my goal is to get SD24s fired as close to the same time.   Do you think this would work?

    * Setup GPIO as interrupt (I want this to be HIGH Priority)

    * ISR will 'kick' SD24 by register write

    * SD24 will sample (how long does this take? ~4 clocks?)

    * ISR will 'turn off' SD24 by register write

    * ISR will clear the interrupt flash and wait ...

  • 0 in reply to pathfinder
    Guru 26200 points
    Hey Marc,
    I did not responded to you because I think that we have similar skills in reading with understanding.
    Glad that Jace H came in.
  • 0 in reply to pathfinder
    TI__Guru 56685 points
    Marc,

    How long the SD24 samples is dependent on your settings, but you wouldn't want to keep in the GPIO ISR for that. You would want to use the SD24 Interrupts to know when it is done sampling (ideally the last channel since they will be slightly offset). Once your last sample is done, then you can do your upkeep actions like reset IFR and reenable the GPIO interrupt if you like.
  • 0 in reply to Jace H
    TI__Genius 12790 points

    Jace,

    I may be being a bit dense on this but how can I align the GPIO interrupt into this sequence.  It may be in the details but i wanted make sure i understand.

    Does this look reasonable or am I off?

  • 0 in reply to pathfinder
    TI__Guru 56685 points
    Marc,

    What you have above is one way to visualize it yes. It look about right as well. I would typically separate out the GPIO ISR and the SD24 ISR, but that's a matter preference I guess.

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