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MSP430F6736 RTC Problem

DHANASEKAR KANDASAMY
Prodigy 20 points
Other Parts Discussed in Thread: MSP430F6736

I am using RTC_C in MSP430F6736 with Auxvcc3 connected with a 3V Battery and the remaining axillary VCCs  not used. RTC_C timing is incremented properly while the unit is powered ON, while the unit is powered off for an hour then powered ON the RTC registers are retaining the values during power off.

During power off state Oscillator is oscillating @ 32.768 KHZ .

Kindly help me to resolve the issue.

  • 0
    Prodigy 20 points

    During power off  "Supply voltage supervisor"  reset the MSP430F6736 after reset thershold voltage level, the reset  value of RTCHOLD bit is 1 in RTCCTL1 which stops the RTC register updation during power off . So I have few questions,

    1. How to Clear RTCHOLD bit during power off?

    2. How to run RTC with Supply voltage supervisor enabled?  

  • 0
    Guru 227245 points

    Unused AUXVCCs should be tied to GND (except for AUXVCC3, which should be tied to VCC) and not left floating.

     RTCHOLD is set during the boot code execution after a POR. You must ensure that at power fail, the MSP is not trying to reboot. If it boots, it must be sure that your code gets as far as clearing the RTCHOLD bit. If the boot process is interrupted before (e.g. by a ‘flickering’ supply), after the first reboot attempt until the one that finally restarts your application, the RTC will be stopped.

     The only way I can think of to prevent this, is to power the AUXVCC1 (e.g. load a capacitor through a diode), so on power fail, you can get an interrupt and prepare the MSP for power-off, then go into LPM3.5 (which will lock the RTC registers, AFAIK). It requires proper programming of the SVS too.

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