model 251 Optical isolation Interface converter Manual
Update: 30 September, 2023
Model 251 is an RTS controlled transmit optically isolated RS-232 to RS-485 interface converter that can convert RS-232 TXD and RXD signals to balanced half-duplex RS-485 signals. On the RS-232 side, Model 251 is powered by 20 pins (DTR) and 4 pins (RTS) control signal lines. DTR must always be set to a high level. RTS must be switched between high level (when transmitting) and low level (when receiving) so that Model 251 can operate normally.
