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MSP430F5438 LPM 3

Shiju C G
Prodigy 145 points

Hi,

I need to implement LPM mode. In which RTC,GPIO,UART should functional. I think LPM 3 can be implemented to meet the requirement.

1.Is LPM 3 meet my requirements?

2.Is it possible work UART at a baud rate of 115200 at this mode?

3.Is it possible to set 3 independent alarm for rtc in this mode?

I  could see that in LPM mode 3 only ACLK is enabled. Using ACLK (32Khz) the maximum baud rate will be 9600. Can anybody suggest any alternative if any?

thanks in advance

  • 0
    Guru 227245 points
    Well, LMP3 could do.
    LMP3 will keep ACLK active. Since you need 32768Hz ACLK for the RTC, you would also only have 32768Hz ACLK for UART in LPM3. Which in most cases won't suffice. 9600Bd with 32768Hz is not very reliable (quite large bit timing error: factor 3.41 means you're almost 1/7 bit off). For reliable operation, You'll likely need a higher clock for UART, on SMCLK then (limiting LPM to 2) and perhaps driven by DCO (limiting LPM to 0).
    GPIO by itself doesn't need a clock, so it works in any LPM. But likely you want more than just a static I/O state. You might need a timer. Or the CPU to change the output state or act on input state. Well, to act on input interrupt, any LPM will do, as an interrupt will wake the CPU (temporarily exiting any LPM). However, the wakeup from LPM>0 has some latency (wakeup time).

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