The clock signal is output to PORTB by using an endless while loop that toggles the port, and hence the clock signal will be divided by 10 (nominal frequency of 3276.8 Hz). All Microchip tinyAVR® devices are supported. To use a 32768 Hz crystal as the clock source for the device, the low-frequency crystal oscillator must be selected by setting CKSEL fuses. Look in the data sheet for details.