Forum Post: MSP430F6779: RTC_C module oscillator failure

Hi,

I try to understand MSP430F6779 mcu and its modules.

I have 32867 Hz external crystal connected to XT1. 

MCLK is fed by DCO stabilized by FLL based XT1.

And LCD clock source is ACLK which is from XT1.

And RTC_C module is fed by external XT1.

I wanted to see what is going on if XT1 fails. I stop it intensionally by touching.

Result:

1. MCLK continued as is, FLL source automatically switched to REFO which is less accurate internal 32Khz source, but it is very nice and acceptable.

2. LCD, it automatically continued working with REFO. I didn't feel anything, no flicker, nothing. Nice.

3. RTC_C, it stopped counting. It just fired RTCOFIFG (failure of the 32kHz crystal oscillator) and didn't continue.

I was expecting that RTC_C will continue counting automatically through REFO in case of external crystal fails. Isn't this the case? Is there a way to tell RTC_C module that continue counting by using REFO?

Thanks.