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CCS/MSP430F5659: MSP430F5659-RTC-B time lag observed even in presence of Battery backup.

Shruti Ingalhalli
Prodigy 10 points
Part Number: MSP430F5659


Tool/software: Code Composer Studio

Hello,

I am using msp430f5659 controller in my product. I am facing issue related to RTC-B time lag. During POR can we switch on to manual switching between Vcc and Vbat?

I am using coin battery for RTC battery backup supply.

As I am implementing PMM module, RTC clock init is performed after PMM setVcore returns true.(Before main function execution starts).

If it returns false, BOR is performed. Due to which RTC is lagging.

My query is, since backup battery is available, even when Dvcc fails,the time should not be lost after POR. 

Thanks,

Shruti

  • 0
    TI__Mastermind 49692 points

    Hello,

    I would recommend referring to our code examples related to the RTC module, such as 'msp430f665x_RTC_01.c' and 'msp430f665x_LPM35_RTC.c'. From your description above, I'm concerned that you're missing something in your setup and configuration code.

    Next, I would recommend reading through Chapter 3 Battery Backup System in the User's Guide to know how to configure the device to either switch automatically between VCC and VBAT or do this manually. There are many things to be aware of for each configuration. For example, if the backup-supplied subsystem is powered by the secondary supply VBAT, the access and control to modules located in the subsystem is restricted. In Section 3.2.1 says that if the backup-supplied subsystem is powered by the secondary supply VBAT the LOCKBAK bit is automatically set. While LOCKBAK=1 it is impossible to access to the information stored in the backup-supplied subsystem. After its supply switched back to the primary supply do the following steps to get access to it :

    1. Initialize the configuration registers of the real-time clock module exactly the same way as they were configured before the switch to the secondary supply.
    2. Clear the LOCKBAK bit in the BAKCTL register.
    3. Check the LOCKBAK bit.
      1. If LOCKBAK = 0, continue with the next step.
      2. If LOCKBAK = 1, the supply for the backup-supplied subsystem has not settled yet. Continue with step 2.
    4. Enable RTC interrupts.
    5. The enabled RTC interrupts will now be serviced as normal interrupts.

    Also, the backup-supplied subsystem (powered by your coin cell battery) is always powered from the secondary supply VBAT if the BAKSW in the Battery Backup Control register BAKCTL is set to 1. A POR resets the BAKSW bit, and the system returns to automatic switch control.

    Hopefully this helps.

    Regards,

    James

    MSP Customer Applications

  • 0
    TI__Mastermind 49692 points

    Also, I'm linking this thread to another thread with nearly the same question to provide the best support in case there are duplicate efforts supporting the same issue.

    Regards,

    James

    MSP Customer Applications

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