The CC3135 device requires two separate clocks for its operation:

• A slow clock running at 32.768 kHz is used for the RTC.
• A fast clock running at 40 MHz is used by the device for the internal processor and the WLAN subsystem.

The device features internal oscillators that enable the use of less-expensive crystals rather than dedicated TCXOs for these clocks. The RTC can also be fed externally to provide reuse of an existing clock on the system and to reduce overall cost.