Furuno FAR21x7 & BB FAR28x7 Operator's Manual BB FAR28x7 Operator's Manual page 275

Serial interface – input ports
Heading sensor
Transmission rate is selectable from 4800 bps and 38.4 kbps.
Isolated RS485 Transceiver
LTC1535
Logical High: A-B> +0.2V
Logical Low: A-B< -0.2V
Log/navigator
Photo Coupler
PC-400
This port is an opticoupler used to isolate I/F terminal on RD terminal.
Absolute maximum rating
Input
Forward current: 50 mA
Reverse voltage: 6 V
Output
Supply voltage: 16 V
High level output voltage: 16 V
Low level output current: 50 mA
RD-A
RD-B
GND
470 ohm
RD-A
RD-B
APPENDIX
AP-27