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Wake-up time from Standby mode(LPM3) on MSP430G2x family.

Kaka
Guru 24520 points


Hi community member,

Please let me confirm the following questions.

[Question.1]

 According to the datasheet,  it said "Ultra-Fast Wake-Up From Standby Mode in Less Than 1 µs".

 Does this performance depend on the clock source? We would like to know whether this time will be varied by using the external digital clock or by using 32k-crystal.

[Question.2]

Does this wake-up time from LPM3 depend on the wake-up source( such as UART, GPIO and source)?

[Question.3]

In case of using the external digital clock or using 32k-Crystal, will  the power consumption of msp430 be increased from in case of using internal clock(VLO)?

If you have any questions, please let me know.

Best regards.

Kaka

  • 0
    Guru 12050 points

    G2x have a simple internal Resistor-Cap DCO, the  benefit of simple (no PLL etc) is that it wake up really fast.

    Though you could route 32k clk or vlo to mclk, it's more beneficial to run it at 1mhz, get the job done fast and go to sleep.

    As any IRQ will kick on the DCO so the msp can run its interrupt, so that if fully automated in hardware and yes it will only take 1 µs. 
    And unless your IRQ_exit change the stack, when IRQ is done it turns DCO back off (if it was off when irq was triggered)

    1 µs is very fast, same a 1 tick of a single cycle asm instructions at 1MHz

    The wake up time is the same for any type of IRQ source
    in slave SPI/i2c mode you can even use lpm4 as the external clk is shifting in the data and when 8 bits are done you get a IRQ  that wakes up the msp.

    You would not use the VLO if you have a 32K crystal
    I don't think you even can if you want to, the VLO will act as a auto-backup if crystal error though

  • 0
    Guru 227245 points
    As Tony pointed out, the wakeup refers to the wakeup time of the DCO. If you leave the DCO running, wakeup is instantly. Same for running MCLK from a different clock source that isn't disabled at all.
    So if you leave the Crystal running during sleep (LFXT1 doesn't consume even a fraction of the DCO), wakeup is instantly.
    Well, since each LFXT1 cycle takes 30µs, wakeup time can be up to 30µs when MCLK is running from LFXT1. :)

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