The program restarts running after 4096 clock from overflow.
4096时钟周期后溢出,晶振12Hz,使用16位寄存器
计算溢出时间为1S的初始值如下:
1S = 1/(12M/4096) * (2^16 - CNT)
1000 000us = 1/(12us/4096) * (65536 -CNT)