This RS232 to RS485 converter is compatible with the RS232C and RS485 standard. It is able to convert RS232 signals to RS485 balanced differential signals and extend the communication distance to 1.2 km. It is a passive converter and doesn't require a external power supply. It uses a particular pump to gain power from the RS232 signals (RTS, DTR, TXD) without initializing the RS232 interface. An internal transceiver circuit automatically controls the direction of the data stream instead of handshake signals. When working in half-duplex mode the circuit keeps the same function under RS485 without any change. The transmission rate of 300 - 115200bps can be applied to point-to-point and point-to-multipoint networks. Overall features Compatibility: EIA/TIA RS232C standard and RS485 standard. Interface RS232 side: DB9 female connector. Interface RS485 side: DB9 male connector with optional terminal board. Working mode: asynchronous, half-duplex, differential transmission. Transmission rate: 300 - 115200bps Recommended transmission media: twisted pair or shielded twisted pair. Mechanical dimensions: 95mm x 33mm x 17mm Working environment: 0 ~ 70¡ãC, relative humidity 5% - 95% Transmission distance: RS485 max. 1200m, RS232 side max. 5m RS232C connector definition   RS485 connector definition DB9 pin no. RS232C singnal 1 DCD 2 RXD 3 TXD 4 DTR 5 GND 6 DSR 7 RTS 8 CTS 9 RI   Pin no. DB9 male Terminal board 1 D-/B D+/A 2 D+/A D-/B 3 - GND 4 - +5V ~ +12V 5 GND - 6 +5V ~ +12V - 7 - - 8 - - 9 - -