1. In the circuit design, for digital input and output port and cable connector pin chips, it is recommended to connect resistance in series of an appropriate size (22 ~ 100 Ohm) in order to protect I/O port. (See below)

2. In PCB layout, we should try to avoid I/O port lays directly in PCB board edge. For I/O port that series connected resistance, the resistance should be close to the pin of chip, in order to achieve optimal protective effect. (See below).