Electronic – What happens to I/O pins in Low Power Mode on MSP430

msp430

I'm reading the datasheet for the MSP430G2553 about the low power modes that the microcontroller has but it doesn't talk about what happens to the IO Ports when it enters low power modes. It only talks about the what happens to the clocks like so:

• Active mode (AM)
– All clocks are active

• Low-power mode 0 (LPM0)
– CPU is disabled
– ACLK and SMCLK remain active, MCLK is disabled

• Low-power mode 1 (LPM1)
– CPU is disabled
– ACLK and SMCLK remain active, MCLK is disabled
– DCO's dc generator is disabled if DCO not used in active mode

• Low-power mode 2 (LPM2)
– CPU is disabled
– MCLK and SMCLK are disabled
– DCO's dc generator remains enabled
– ACLK remains active

• Low-power mode 3 (LPM3)
– CPU is disabled
– MCLK and SMCLK are disabled
– DCO's dc generator is disabled
– ACLK remains active

• Low-power mode 4 (LPM4)
– CPU is disabled
– ACLK is disabled
– MCLK and SMCLK are disabled DCO's dc generator is disabled Crystal oscillator is stopped

So what happens to the IO ports? Is it a given that they remain in the state before it enters the low power mode?

Best Answer

A lot isn't explained in the chip's own datasheet. With 450 processor models, this makes perfect sense : the datasheet describes the chip-specific stuff; common information is refactored out into a user manual covering the entire family of devices.

The user manual for that device family is

MSP430x2xx Family User's Guide

Literature Number: SLAU144J

Operating modes, ch 2.3, p.38 says:

When setting any of the mode-control bits, the selected operating mode takes effect immediately (see Figure 2-9). Peripherals operating with any disabled clock are disabled until the clock becomes active. The peripherals may also be disabled with their individual control register settings. All I/O port pins and RAM/registers are unchanged. Wake up is possible through all enabled interrupts.

So, the I/O pins retain their current function and (for output pins) values.

In other words if you're trying to save power, any power they are supplying to LEDs etc is your problem (turn them off, along with peripherals you don't need, before sleeping).

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