SELS Bit 3 Select SMCLK. This bit selects the SMCLK source.
0 DCOCLK
1 XT2CLK when XT2 oscillator present on-chip. LFXT1CLK when XT2
oscillator not present on-chip.
你把xt2关了之后 SMCLK选的是低频时钟源 32k的那个 但是你要是给xt2开开 就是8M的时钟源了
所以功耗就上去了另外 关闭XT2晶振 是 BCSCTL1 | =XT2OFF