Depending on the architecture, four external clock sources drive two major power consuming blocks. There are two low-speed clocks; one for the sleep clock and the other for the RTC. The 16MHz clock source drives the MCU and its peripherals. The 24MHz clock source drives the low power wireless transceiver SoC (System on Chip). The BLE (Bluetooth Low Energy) protocol, as the ubiquitous low power wireless protocol, uses a cyclic sleep scenario to conserve power.