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. 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). It is compatible with current communication software and hardware, no need to set the previous working mode which base on RS-232. This guarantees that there is no need to modify the programming under RS-232 half duplex mode; 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.