GE Interlogix Calibur CBR-PB3-WD Installation Manual page 12

Termination Switch
Termination is set on SW4 for PORT 0 (Dipswitch #3)
termination on some of the PB3 units will change. The first PB3 and the last
PB3 on the RS-485 network will have termination set to ON (Down), all
others between these two units will have their termination set to OFF (Up).
Sample Systems Termination:
Kalatel CBR-PB3-WD
Termination is important whenever multiple PB3
units are interconnected via the unit's built-in RS-
485 network. The default termination setting on the
ProBridge 3 unit is with termination set to ON.
Whenever there are more than two PB3's,
12 0150-0261A