For communication between PC with different standard serial port and external equipments or intelligent instruments, standard serial conversion is necessary. This converter is compatible with RS-232C, RS-485 standards. It converts RS-232 signals into balanced differential RS-485 signals. This converter is designed to protect RS-485 port; it adopts advanced TVS (TRANSIENT VOLTAGE SUPPRESSOR). The transmission distance of RS-232 communication can be extended to 1.2km. It adopts unique “RS-232” charge pump technology to drive the system, and gains power without initializing RS-232 serial port. This converter is with built-in zero delay auto receiving and transmitting conversion and unique I/O circuit auto control data flow direction without any handshake signal (RTU, DTR); this guarantees that there is no need to modify the programming under RS-232, it will run smoothly under current software and hardware. The transmission rate is 300-115.2kbps. It can be used between hosts, host and SCM, which building a point to point, point to multipoint long-distance communication networking. It is widely applied in industrial automation control system, all-in-one card, access control system, parking system, ATM system, bus charging system, canteen ticketing system, attendance system, and toll station system, etc.