Low Power Modes (LPMs) represents the ability to scale the microcontroller’s power usage by shutting off parts of the MSP430. The CPU and several other modules such as clocks are not always needed. Many applications which wait until a sensor detects a certain event can benefit from turning off unused (but still running) parts of the microcontroller to save energy, turning them back on quickly when needed.

Each subsequent LPM in the MSP430 turns off more and more modules or parts of the microcontroller, the CPU, clocks and . T covers the LPM modes available in the MSP430F1611, which are similar to the ones available in most MSP430 derivatives. For the most accurate information, refer to the User’s Guide and Datasheet of your particular derivative. Not mentioned here are LPM5 and some other specialized LPMs. These are available only in select MSP430 devices (in particular the newer F5xx series). However, the basic idea behind LPMs is the same, i.e. gradual shut down of the microcontroller segments to achieve power reduction. Active - Nothing is turned off (except maybe individual peripheral modules). No power savings

  1. LPM0 - CPU and MCLK are disabled while SMCLK and ACLK remain active
  2. LPM1 - CPU and MCLK are disabled, and DCO and DC generator are disabled if the DCO is not used for SMCLK. ACLK is active
  3. LPM2- CPU, MCLK, SMCLK, DCO are disabled DC generator remains enabled. ACLK is active
  4. LPM3 - CPU, MCLK, SMCLK, DCO are disabled, DC generator is disabled, ACLK is active
  5. LPM4 - CPU and all clocks disabled

It is important to note that once parts of the microcontroller are shut off, they willIt is important to note that once parts of the microcontroller are shut off, they will not operate until specifically turned on again. However, we can exit a low power mode (and turn these parts back on), and interrupts are extremely useful in this respect. Another Low Power Mode, LPM5, is available in some derivatives of the MSP430

As an example of the savings that can be achieved by incorporating Low Power Modes into the software design, I present Figure 9.1, which is shown in the MSP430F2274 User’s Guide: We usually enter a low power mode with the interrupts enabled. If we don’t, we will not be able to wake up the system.

Low Power Mode Savings

The x represents LPMs from 0 to 4 in the MSP430F2274. Another important thing to know is that the low power modes don’t power down any modules such as the ADC or timers and these must be turned off individually. This is because we might want to combine the low power mode with them.

A simple example is going in a Low Power Mode while the ADC is sampling and then waking up from the ADC interrupt when the sample has been obtained.