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CCS/MSPCAPTDSNCTR: CapTIvate wake up LPM4.

Peter Kostadinov
Prodigy 230 points
Part Number: MSPCAPTDSNCTR
Other Parts Discussed in Thread: MSP430FR2633

Tool/software: Code Composer Studio

Hi,

I use MSP Captivate Dev. Board (msp430fr2633) to research capticate periphery. In  file:///C:/ti/CapTIvateDesignCenter_1.60.00.00/CapTIvateDesignCenter/docs/users_guide/html/CapTIvate_Technology_Guide_html/markdown/ch_library.html I found following - "The low power mode may be LPM0 to LPM3. The function returns when all measurements and processing are complete.". But in the  document "slas942b.pdf" there is "Table 6-1. Operating Modes" in which is explained that LPM4 mode can be wake-up by IO and also by CapTIvate. I tested one of the example projects with changed LPM3 to LPM4 and it continue to work normally. 

Is it error in the web page or I have some mistake in my tests.

Best Regards,

Peter

  • 0
    TI__Expert 7530 points
    Hi Peter,

    CapTIvate can be used in active mode, LPM0, LPM3, and LPM4. There are two aspects to configuring the low power modes: the LPM selected during the conversion itself, and the LPM selected in between conversions. The documentation line which you reference is referring to the LPM parameter passed to the CAPT_updateSensor(), CAPT_updateSensorWithEMC(), or CAPT_updateSensorRawCount() functions. This tells the MCU which LPM to enter during the capacitance-to-digital conversion itself while the CPU waits for the conversion to finish so that it can read out the results. You could manually set this to LPM4 without consequence to the CapTIvate functionality. However, you may notice that the power consumption is not significantly different between LPM4 and LPM3 in this case, as the power used by CapTIvate during the conversion can be quite high. So, to answer your question, the documentation is not inaccurate so much as it is limited. It doesn't list LPM4 as supported, but you can use LPM4. However, there is not significant benefit to running in LPM4 during the conversion itself.

    If you are attempting to optimize a design for low power, you will want to optimize the CapTIvate scan time to be as short as possible, and also increase the scanning interval (the time in between scans).

    If you haven't already seen it, check out the low power design guide here:
    http://www.ti.com/captivateulp

    This discusses the important optimization information to achieve a low power design. If you only have a few buttons in your design, you can configure the MCU to go into LPM4 with CapTIvate running autonomously until a detection occurs. This can save quite a bit of power.

    Let us know what questions you have!

    Regards,
    Walter
  • 0 in reply to Walter Schnoor
    Prodigy 230 points
    Hi Walter,
    Thank you very much for your fast and accurate answer!
    Best Regards,
    Peter

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