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MSP430FR2433: will UART prevent system from entering LPM3 or LPM4?

Zhiyong Li (FT)
Expert 2920 points
Part Number: MSP430FR2433
Other Parts Discussed in Thread: ENERGYTRACE

Hi,

One of our MSP430FR2433 based device still draws ~500uA current when it is supposedly in LPM3, a lot higher than the number specified in datasheet. UART module is still active before system attempts enter into LPM3.

__bis_SR_register(LPM3_bits | GIE); // Enter LPM3

So my question is, will active UART with RX interrupt enabled prevent system from entering LPM3? I suppose so, because UART in FT2433 sources clock from SMCLK, which can draw considerable amount of current itself. Is so, what is the proper way to turn of UART module before entering LPM3?

Thanks,

ZL

  • 0
    TI__Mastermind 23295 points

    Hi ZL

    The current of LPM3 can't be tested at the debug mode.

    You can confirm all GPIO no connection and output H or L.

    Then, disconnect FET， Let MCU free run and test the power consumption of low power mode

    Thanks

  • 0 in reply to Xiaodong LI
    Expert 2920 points

    Hi,

    Thanks for your response. The test was not done in debug mode. Firmware was loaded into MSPFR2433 then device was tested with EnergyTrace on CC1352P1-launchpad.

    Could you comment on if UART with Rx interrupt enabled will prevent system from entering into LPM3 or LPM4? In one of the posts I stumbled upon, it is said that we should set the UART pins to GPIO before entering into LPM3/4. Somehow I don't see any difference after doing that.

    Best,

    ZL

  • +1
    Guru 25105 points

    An active UART will submit a clock request which will activate its clock source. So an active clock will keep the system out of an LPM mode that disables that clock. An idle clock will not. There is a bit you can clear to disable this. (SMCLKREQEN)

    Note that while the UART will start up when it senses a start bit, the timing will be wrong since the clock takes time to start up. So the first data received could have errors.

  • 0 in reply to David Schultz
    Expert 2920 points

    Hi Mr. Schultz,

    Thanks again for answering my questions. To clarify, my understanding is this: unless UART is actively receiving data, just having RX interrupt enabled won't prevent system from entering LPM3/4. Regarding error in first received data, this indeed can be a problem. We encountered it in other MSP430 devices.

    Best,

    ZL

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