SWRU626 December 2025 CC3501E , CC3551E
The RTC is a 67-bit, 2-channel timer running on the LFCLK system clock (see Section 7.3.2.2). The RTC is active in SLEEP and ACTIVE power states. When the device enters SHUTDOWN state the RTC is reset.
RTC is reset when device resets (reset pin, WDT, debug request reset). The RTC is not reset when Host MCU is executing SOC AON reset.
The RTC accumulates time elapsed since reset on each LFCLK. For better accuracy the source LFCLK is averaged by the RTC filter, generating clock signals LFTICK and LFINC. The RTC counter is incremented by LFINC at a rate of 32.768 kHz. LFINC indicates the period of LFCLK in μs, with an additional granularity of 16 fractional bits.
The counter can be read from two 32-bit registers. RTC.TIME8U has a range of approximately 9.5 hours with an LSB representing 8 microseconds. RTC.TIME524M has a range of approximately 71.4 years with an LSB representing 524 milliseconds.
There is hardware synchronization between the system timer (SYSTIM) and the RTC so that the multi-channel and higher resolution SYSTIM remain in synchronization with the RTC’s time base.
The RTC has two channels: one compare channel and one capture channel and is capable of waking the device out of the sleep power state. The RTC compare channel is typically used only by system software and only during the sleep power state.