Forum Post: RE: Clock switching from DCOCLKDIV to XT2 and back to DCOCLKDIV

XT1 and DCOCLKDIV are two different clocks. (It appears you are using XT1 as the reference clock for the FLL.) Anyway, to change the SMCLK source, change the SELS field in the UCSCTL4 register: UCSCTL4 = (UCSCTL4 & ~SELS_7) | SELS__DCOCLKDIV;