Operating Modes
59
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
System Resets, Interrupts, and Operating Modes, System Control Module
(SYS)
(1)
The abbreviation "LPMx.5" is used in this document to indicate both LPM3.5 and LPM4.5.
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 Low-Power Modes LPM3.5 and LPM4.5 (LPMx.5)
The low-power modes LPM3.5 and LPM4.5 (LPMx.5
(1)
) give the lowest power consumption on a device.
In LPMx.5, the core LDO of the device is switched off. This has the following effects:
•
Most of the modules are powered down.
–
In LPM3.5, only modules powered by the RTC LDO continue to operate. At least an RTC module is
connected to the RTC LDO. Refer to the device's data sheet for other modules (if any) that are
connected to the RTC LDO.
–
In LPM4.5 the RTC LDO and the connected modules are switched off.
•
The register content of all modules and the CPU is lost.
•
The SRAM content is lost.
•
A wake-up from LPMx.5 causes a complete reset of the core.
•
The application must initialize the complete device after a wake-up from LPMx.5.
The wake-up time from LPMx.5 is much longer than the wake-up time from any other power mode (see
the device-specific data sheet). This is because the core domain must power up and the device internal
initialization must be done. In addition, the application must be initialized again. Therefore, use LPMx.5
only when the application is in LPMx.5 for a long time.