4.5.2 Low-Frequency Oscillators

Modify the customer configuration area to select the low-frequency clock source. The application must ensure that the LF clock source selected in CCFG is selected and stable before entering standby mode. The LF clock source on which the device is running can be read through the driverlib function OSCClockSourceGet(…). For the configuration settings in CCFG, see Figure 16.

Figure 16. LF Configuration in ccfg.c

When the device running on the selected LF clock source as specified in CCFG, you must disable the LF clock qualifier circuitry before entering standby for the first time. Set bits OSC_DIG:CTL0[29:28] as in Figure 17.

Figure 17. Code for Disabling LF Clock Qualifiers

If the application wants to use an external LF clock source, another MCU can apply the LF clock to any input and output pin.

1. Configure the chosen input and output and the RTC increment value as in Figure 18.
2. Apply when trimDevice() runs.

An RTC increment value of 0x800000 corresponds to a frequency of 32.768 kHz. See AON_RTC:SUBSECINC for further details.

Figure 18. Configuration When Using an External LF Clock Source