
Operating Modes
1.4.2 Entering and Exiting Low-Power Modes LPM0 Through LPM4
An enabled interrupt event wakes the device from low-power operating modes LPM0 through LPM4. The
program flow for exiting LPM0 through LPM4 is:
•
Enter interrupt service routine
–
The PC and SR are stored on the stack.
–
The CPUOFF, SCG1, and OSCOFF bits are automatically reset.
•
Options for returning from the interrupt service routine
–
The original SR is popped from the stack, restoring the previous operating mode.
–
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+SCG1+SCG0,SR
; Enter LPM3
;
...
; Program stops here
;
; Exit LPM3 Interrupt Service Routine
BIC
#SCG1+SCG0,0(SP)
; Exit LPM3 on RETI
RETI
; Enter LPM4 Example
BIS
#GIE+SCG1+SCG0,SR
; Enter LPM4
;
...
; Program stops here
;
; Exit LPM4 Interrupt Service Routine
BIC
#SCG1+SCG0,0(SP)
; Exit LPM4 on RETI
RETI
1.4.3 Entering and Exiting Low-Power Modes LPMx.5
LPMx.5 entry and exit is handled differently than the other low power modes. LPMx.5, when used
properly, gives the lowest power consumption available on a device. To achieve this, entry to LPMx.5
disables the LDO of the PMM module, which removes the supply voltage from the core of the device.
Because the supply voltage is removed from the core, all register contents and SRAM contents are lost.
Exit from LPMx.5 causes a BOR event, which forces a complete reset of the system. Therefore, it is the
application's responsibility to properly reconfigure the device upon exit from LPMx.5.
The wakeup time from LPMx.5 is significantly longer than the wakeup time from the other power modes
(see the device-specific data sheet). This is primarily because, on exit from LPMx.5, time is required for
the core voltage supply to be regenerated and for boot code execution to complete before the application
code can begin. Therefore, the use of LPMx.5 is restricted to very low duty cycle events.
There are two LPMx.5 power modes, LPM3.5 and LPM4.5. LPM4.5 allows for the lowest power
consumption available. No clock sources are active during LPM4.5. LPM3.5 is similar to LPM4.5, but has
the additional capability of having a RTC mode available. In addition to the wakeup events possible in
LPM4.5, RTC wakeup events are also possible in LPM3.5.
38
System Resets, Interrupts, and Operating Modes, System Control Module
SLAU272C – May 2011 – Revised November 2013
(SYS)
Copyright © 2011–2013, Texas Instruments Incorporated