Q: It was found that there was a periodic change in the waveform shape at PIN1 X1. The duty cycle of PIN7 SQW/OUT varied between 57% to 97% when a probe was also placed at PIN1. However, when the probe at PIN1 was removed, the duty cycle of PIN7 SQW/OUT was between 69% to 71%.
A:
1. If PIN1 is not connected to the probe, there is smaller variation in the waveform, indicating that the cause of this problem is the addition of probe load on PIN1.
2. If we need to verify whether or not the crystal is operating normally, it must be determined by measuring the waveform of PIN7. If there is no problem in the waveform of PIN7, the crystal is operating normally. If there is still some problem with the waveform of PIN7, there may be something wrong with the crystal. According to the description in the data sheet, a crystal with load capacitance of 6pF must be used as the external crystal of DS1339. A proper crystal should be selected and connected according to the instructions in the data sheet. The crystal should be as close to the device pin as possible. Usually there will be no problem.