What's the max frequency of MCLK when connecting 32768Hz at XT1(MSP430F5419A)

Download code examples www.ti.com/.../slac375 and check msp430x54xA_UCS_x files for DCO setup.

MCLK can go over 25 MHz, but from my experience using directly XT2 for overclocking is better choice. I am running some MSP430F5510 boards at 48 MHz MCLK directly from XT2 48 MHz crystal.

http://forum.43oh.com/topic/3909-msp430f550x-based-logic-analyzer/?p=69255

The 25 MHz value is not calculated; it is the maximum frequency at which TI guarantees the core does not overheat. (Section 5.20 of the datasheet shows that with DCORSELx=7 and DCOx=31, you could get at least 60 MHz.)

To run the DCO at 25 MHz, use XT1 as reference for the FLL, and configure the FLL with a multiplier of 763.