1. The DS1307 has an internal resonant circuit; the X1 and X2 should not be connected to any additional resistors or capacitors.
2. The crystal's load capacitor has to be 12.5pF, with a maximum ESR of 45K. Choose suitable crystal bodies.
3. When verifying whether the crystal is resonating, do not use the oscilloscope to directly measure the crystal's pin since the oscilloscope's input capacitor may sometimes cause the resonator to malfunction. The correct method is to setup the SQW input internal clock signal, then measure the output signal to discern whether the clock is operating.
2. The crystal's load capacitor has to be 12.5pF, with a maximum ESR of 45K. Choose suitable crystal bodies.
3. When verifying whether the crystal is resonating, do not use the oscilloscope to directly measure the crystal's pin since the oscilloscope's input capacitor may sometimes cause the resonator to malfunction. The correct method is to setup the SQW input internal clock signal, then measure the output signal to discern whether the clock is operating.