XT1 fault - SELA bits

Todd Anderson78572

All:

F5528 - if I force an XT1 fault (by shorting the crystal, I get the XT1LFOFFG bit on in the UCSCTL7 register - at which point, the oscillator is forced to REFO, confirmed by observing ACLK on P1.0 - however, I would also expect the SELA bits to change, showing that REFO is now being used rather than XT1. Is this expected behavior?

over 9 years ago

0 DavidL over 9 years ago

TI__Mastermind 25045 points

Todd,

I'm looking into this.

Regards,

David

0 DavidL over 9 years ago

TI__Mastermind 25045 points

Todd,

That is the expected behaivor. Please read below.

5.2.12 UCS Module Fail-Safe Operation - http://www.ti.com/lit/ug/slau208n/slau208n.pdf

Regards,

David

0 Jens-Michael Gross over 9 years ago

Guru 227245 points

The SELA bits show your (intentional) selection, it does not (alone by itself) reflect the current clock system state. The fault bit shows you what the clock system thinks about your selection :)
As soon as the fault bits are clear (including OFIFG), ACLK will switch back to what is selected with SELA.
This is also explained in the fault mechanism description in the users guide.

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XT1 fault - SELA bits