SPRUJF2A March 2026 – March 2026 AM13E23019
LFCLK provides a continuous 32kHz clock to a variety of peripherals on the device. After a BOOTRST, LFCLK is sourced by the internal 32kHz oscillator (LFOSC).
LFCLK is active in RUN, SLEEP, STOP, and STANDBY power modes. It is possible to disable both ULPCLK and LFCLK together to most peripherals in STANDBY mode to achieve the lowest possible STANDBY mode power consumption (STANDBY1). To do so, set the STOPCLKSTBY bit in the MCLKCFG register in SYSCTL before entering STANDBY. In this state, a few times are the only clocked peripherals.
LFCLK is a synchronized clock. All LFCLK edges are synchronized to the main system clocks (MCLK and ULPCLK), meaning that the registers of peripherals clocked by LFCLK can be read or written to at any time without any special handling.When MCLK/ULPCLK are not sourced by LFCLK (for example, when they are sourced by SYSOSC) there is a 5 ULPCLK cycle synchronization delay between the low frequency clock source's clock edge and the corresponding LFCLK edge as seen by peripherals running from LFCLK.
When the MCLK/ULPCLK frequency is constant, this delay is constant and it does not add jitter to LFCLK. If the MCLK/ULPCLK frequency changes, the synchronization delay changes proportionally and this results in a small single-cycle LFCLK jitter at the MCLK/ULPCLK frequency transition point. This jitter changes the duty cycle of one LFCLK period, but there is no accumulation of error (there is never a change in the number of LFCLK periods, ensuring an accurate LFCLK time base for peripherals).