void Enter_Sleep( void )
{

 /*** Sleep Mode is STANDBY ***/
 PM->SLEEPCFG.bit.SLEEPMODE = PM_SLEEPCFG_SLEEPMODE_STANDBY_Val;

 //Ensure register is written before issuing wfi command
 while(PM->SLEEPCFG.bit.SLEEPMODE!=PM_SLEEPCFG_SLEEPMODE_STANDBY_Val);

 // WAIT FOR IRQ
 __WFI();    
}