Hi John,
What is the Vcc supply voltage and what is the voltage level of your external clock?
When XT2 is sourced with an external signal, the voltage level must meet the datasheet parameters.
[quote user="John Wang3"] UCSCTL6 &= ~(XT2OFF & XT2DRIVE_3); // enable XT2[/quote]
XT2 is powered down when used in bypass mode. You can use the below instructions to enable the Bypass mode.
P5SEL |= BIT2; // Port select XT2
UCSCTL6 |= XT2BYPASS; // Set XT2 in Bypass mode
From your code tt seems that you want to run the CPU (MCLK) at 6 MHz (DIVM_2). Is that your intention?
Regards,
Mo.