/* Set PLL to power down mode and PLL_STB bit in CLKSTATUS register will be cleared by hardware.*/
SYSCLK->PLLCON|= SYSCLK_PLLCON_PD_Msk;
/* Set PLL frequency */
SYSCLK->PLLCON = PLLCON_SETTING;
/* Waiting for clock ready */
SYS_WaitingForClockReady(SYSCLK_CLKSTATUS_PLL_STB_Msk);