At the top are all of the control registers to set up the real-time counter and registers to set up the alarm time to wake up the controller. The real-time counter can select between the sub-system clocks; which are typically an external 32kHz crystal or the internal low-speed oscillator, which is usually 15kHz. There is also a Sub-Clock Count register and a preceding Watch Error Correction register which will be explained in a bit more in detail on the next slide.