The Asynchronous Timer clock allows the Asynchronous Timer/Counter to be clocked directly from an external 32 kHz clock crystal. The dedicated clock domain allows using this Timer/Counter as a real-time counter even when the device is in Sleep mode. The Asynchronous Timer/Counter uses the same XTAL pins as the CPU main clock but requires a CPU main clock frequency of more than four times the oscillator frequency. Thus, asynchronous operation is only available while the chip is clocked on the internal oscillator.