Texas Instruments MSP430x1xx manual Entering and Exiting Low-Power Modes

Operating Modes

2.3.1Entering and Exiting Low-Power Modes

An enabled interrupt event wakes the MSP430 from any of the low-power operating modes. The program flow is:

-Enter interrupt service routine:

J The PC and SR are stored on the stack

J The CPUOFF, SCG1, and OSCOFF bits are automatically reset

-Options for returning from the interrupt service routine:

J The original SR is popped from the stack, restoring the previous operating mode.

J The SR bits stored on the stack can be modified within the interrupt service routine returning to a different operating mode when the RETI instruction is executed.

; Enter LPM0 Example
BIS	#GIE+CPUOFF,SR	; Enter LPM0
; ...		; Program stops here
;
; Exit LPM0 Interrupt Service Routine
BIC	#CPUOFF,0(SP)	; Exit LPM0 on RETI
RETI
; Enter LPM3 Example
BIS	#GIE+CPUOFF+SCG1+SCG0,SR	; Enter LPM3
; ...		; Program stops here

;
;	Exit LPM3 Interrupt Service Routine
	BIC	#CPUOFF+SCG1+SCG0,0(SP) ; Exit LPM3 on RETI
	RETI

Extended Time in Low-Power Modes

The negative temperature coefficient of the DCO should be considered when the DCO is disabled for extended low-power mode periods. If the temperature changes significantly, the DCO frequency at wake-up may be significantly different from when the low-power mode was entered and may be out of the specified operating range. To avoid this, the DCO can be set to it lowest value before entering the low-power mode for extended periods of time where temperature can change.

; Enter LPM4 Example with lowest DCO Setting

BIC	#RSEL2+RSEL1+RSEL0,&BCSCTL1	;	Lowest RSEL
BIS	#GIE+CPUOFF+OSCOFF+SCG1+SCG0,SR ;		Enter LPM4
; ...		;	Program stops
;
; Interrupt Service Routine
BIC	#CPUOFF+OSCOFF+SCG1+SCG0,0(SR); Exit LPM4 on RETI
RETI

2-16System Resets, Interrupts, and Operating Modes