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MSP430F149低功耗模式LPM3串口唤醒问题

yun li4
Prodigy 190 points
Other Parts Discussed in Thread: MSP430F149

本人接触MSP430不久，正在做一个低功耗的采集模块，想工作于LPM3模式下，因要操作flash必须用8M晶振，就想在电路上省掉32768HZ晶振，全部都用8M分频，经程序测试如果MCLK和SMCLK都关闭时，串口接收中断无法唤醒，所以请教LPM3模式下如果不用ACLK，串口接收中断就不能使用，必须串口时钟工作才能进入中断？

  • 0
    Expert 1415 points

    yun li4 说：
    因要操作flash必须用8M晶振

    I do not understand why Flash operation needs 8 MHz crystal.

    yun li4 说：
    请教LPM3模式下如果不用ACLK，串口接收中断就不能使用，必须串口时钟工作才能进入中断？

    LPM3 simply means stop MCLK and CPU, stop SMCLK and things that depend on SMCLK. Serial port needs either ACLK or SMCLK to function. If you do not have either ACLK or SMCLK, Serial port cannot function. If it cannot function, it cannot generate interrupts.

    Over all speaking, I do not understand why you chose MSP430F149. There are other chips that may be better for the job.

  • 0 回复 Lichen Wang
    Prodigy 190 points

    操作flash需要257K~476K，两三小时操作一次，ACLK外接高频晶振在LPM3模式一直开着功耗应该会变大，考虑用XT2或DCO分频，担心DCO没有外部晶振准确，所以用8M分频，三小时开个十几ms对功耗应该没啥影响吧

  • 0 回复 yun li4
    Expert 1415 points

    yun li4 说：
    操作flash需要257K~476K

    That means +/- 30% is accurate enough. Very easy to do with DCO. For example, if SMCLK is from DCO set to between 600 and 900 kHz, Use FN=1 to divide by (1+1)=2 will result in a fFTG of between 300 and 450 kHz, well within the the acceptable range.

    Using DCO for Flash operation has the additional advantage of being safer. Because no external component (such as a finicky crystal), is used, DCO is less likely to stop or fail.

    A watch crystal at XT1 can be used to improve the accuracy of by software FLL. Other MSP430 chips may have hardware FLL. MSP430FRxxxx chips have factory Laser trimmed DCO.