Furuno RD-50 Operator's Manual page 84

APPENDIX 4 DIGITAL INTERFACE
Serial Interface
Baud rate is selectable from 4800 bps and 38400 bps. Complies with IEC 61162-2.
Input port (RD-A, RD-B)
Photo Coupler
PC400
Logical High: A-B> +0.2V
Logical Low: A-B< -0.2V
Output port (TD-A, TD-B)
RS485 Transceiver
SN65LBC176
Logical High: A-B> +0.2V
Logical Low: A-B< -0.2V
AP-14
RD-A
RD-B
GND
TD-A
TD-B
GND