• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 80 subscribers
  • Views 6084 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

what exactly is the difference between LPM2 and LPM3?

rahul sreedharan
Prodigy 220 points

1) in LPM1,Is SMCLK active ?

    Is  SMCLK inactive because  DCO and DC generator are disabled.If i have configured the clock module to source SMCLK from LFXT1 or XT2 will it be active in         SMCLK?

2) what exactly is the difference between LPM2 and LPM3?

In LPM2 -DCO - is disabled but DC generator is running 

In LPM3- DCO  is disabled and  DC generator is  disabled.

if DCO is disabled what is the point of running DC generator.

  • 0
    Guru 16361 points

    1) SMCLK will be active if it's not sourced from the DCO. This is only really useful if ACLK can't be used for some reason (eg program needs to use XT1 and XT2).

    EDIT: Ignore that... I needed to read the user's guide again!

    1. It depends which MSP430 family you're using. On MSP430x2xx, SMCLK is turned off in LPM2 irrespective of its source. F5, F6, FR5 and FR6 series allow peripherals to request clocks even if they've been disabled by the current power mode.
    2. As I understand it, leaving the DC generator on reduces start-up time when returning to active mode.

  • 0 in reply to Robert Cowsill
    Guru 227245 points
    LPM3 is turning SMCLK off.
    LPM1 and LPM2 are variants of LPM0 which deactivate the DCO (if not required), LPM1 deactivating just the oscillator, LPM2 deactivating the DC BIAS generator too. Which means it will take even longer to fire it up again on an interrupt.

    Well, after all, there are no "low power modes" at all.
    The LPM macros are just predefined combinations of bits to be set in the status register. Which have individual or combined effects. The meaning varies across MSP families.
    Besides LPM0..4, 11 more combinations of the power control bits are possible, but not always useful.
    For example, you may disable SMCLK and ACLK but keep MCLK active. Will preserve some power too, if your app likes it. The clocks are reactivated on an interrupt while the CPU continues running. You may even disable the DCO this way if MCLK runs from a crystal. (isn't done automatically, as the CPU doesn't know whether you might need the DCO instantly again)

**Attention** This is a public forum