4-Wire Line, Point-To-Point; 4-Wire Line, Multi-Drop - semaphore KINGFISHER PLUS+ Hardware Reference Manual

Kingfisher Plus+ Hardware Manual

6.8.5 4-Wire Line, point-to-point

Either RTU can transmit/receive at any time.
Note: line termination is required.

6.8.6 4-Wire Line, multi-drop

Master RTU can transmit/receive to any one outstation RTU at any time or each outstation
can transmit/receive to master RTU, one at a time.
Note that outstations cannot communicate to each other.
Hardware Manual Version 7.16 http://www.servelec-semaphore.com/ Page 110