Introduction - If you have any usage issues, please Google them yourself
At present, the more commonly used 9-pin serial port serial port (DB9) and 25-pin serial port (DB25), when the communication distance of more recent (<12m), can be directly connected to standard power cable RS232 port (RS422, RS485 away), If the distance required to attach a modem (MODEM). The most simple and commonly used is a three-wire connection, that is, the receive data and send data three-connected, this article only relates to the most basic access method, and directly connected to RS232