SLAZ266AC October   2012  – August 2021 MSP430F5309

 

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6.51 UCS6

UCS Module

Category

Functional

Function

USCI source clock does not turn off in LPM3/4 when UART is idle

Description

The USCI clock source (ACLK/SMCLK) remains enabled in LPM3 and LPM4 when the USCI is configured in UART mode and the communication is idle (UCSWRST = 0 but no TX or RX currently executing). This is contrary to the expected automatic clock activation described in the User's Guide and can lead to higher current consumption in low power modes, depending on the oscillator that feeds ACLK / SMCLK.

Workaround

Use the oscillator that is already active in LPM3 (ACLK) to source the USCI and utilize the low-power baud rate generator (UCOS16 = 0). For UART baud rates where a fast SMCLK sourced by the internal DCO is required use LPM0 instead of LPM3.