SLAZ332AC October   2012  – September 2021 MSP430F6634

 

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6.30 PMM12

PMM Module

Category

Functional

Function

SMCLK comesup fast on exit from LPM3 and LPM4

Description

The DCO exceeds the programmed frequency of operationon exit from LPM3 and LPM4 for up to 6 us. When SMCLK is sourced by the DCO, it is not masked on exit from LPM3 or LPM4. Therefore, SMCLK exceeds the programmed frequency of operation on exit from LPM3 and LPM4 for up to 6 us. The increased frequency has the potential to change the expected timing behavior of peripherals that select SMCLK as the clock source.

Workaround

- Use XT2 as the SMCLK oscillator source instead of the DCO

or

- Do not disable the clock request bit for SMCLKREQEN in the Unified Clock System Control 8 Register (UCSCTL8). This means that all modules that depend on SMCLK to operate successfully should be halted or disabled before entering LPM3 or LPM4. If the increased frequency prevents the proper function of an affected module, wait 32, 48, 64 or 80 cycles for core voltage levels 0, 1, 2, or 3, respectively, before re-enabling the module. (for example,  __delay_cycles(32)