... supply needed. 1, Plug and play, small volume, easy installation 2, Port-powered, high efficiency obtain electricity, can also worked on 3 ... D+, D-, GND Asynchronism, point to point or multi point,2 wire half-duplex Automatic send data control, auto distinguish and ... needed, powered from TXD, RTS, DTR signal in RS-232 port Consumption: Static consumption less than 20mA, dynamic consumption less than ...