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msp430 uart wakeup LPM3

LIN KUO chin
Prodigy 10 points

Dear Sir : 

 we use F2272 MCU stay in LMP3 mode  and waiting the uart  RX interupt to  wakeup MCU ,

the uart  use  Aclk(32768HZ)  for Uart clock ,and baudrate is 9600 , now is work well ,  

and my problem is ,

1. the UART baudrate need to  change 19200,  and use SMCLK  to  for Uart clk ,

  we still need stay in  LPM1 ( or the most low power cumpostion ),

 if not change the H/W ( ACLK- 32768hz),

 and  can we use ISR same code  (exit  LMP3 comand ) to wakup  LPM1 from  RX PIN interrupt ?

2.  any idel  to reverse UART out use the soft  setting ?

   

  • 0
    Guru 227245 points

    Kuo Chin Lin said:
    1. the UART baudrate need to  change 19200,  and use SMCLK  to  for Uart clk ,

    When you use SMCLK, you should be sure of SMCLK frequency.
    The clock divider that was originally dividing 32768Hz into 9600Hz has to be changed properly to match the SMCLK/19200Bd ratio.

    Kuo Chin Lin said:
     if not change the H/W ( ACLK- 32768hz),

    The crystla is no longer needed and can be discarded to save its operatign current - unless you need it for something else.

    Kuo Chin Lin said:
     and  can we use ISR same code  (exit  LMP3 comand ) to wakup  LPM1 from  RX PIN interrupt ?

    I'd rather try an exit LPM1 command instead :)
    However, IIRC it makes no harm, as LPM3 jsut sets some more bits than LPM1 and clearign them when they haven't been set, is not a problem.

    However, when you source SMCLK from DCO and use SMCLK for clockign the UART, then you cannot use LPM1 at all, as you cannot switch off the DCO and still use it :)
    LPM0 is as far as you can go then.

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