GFK-0825F Chapter 3 Installation 3-11
3
Making Bus Connections
1. Connect Serial 1 to the Serial 1 terminals of the previous device and the next device.
2. Connect Serial 2 to the Serial 2 terminals of the previous device and the next device.
3. Connect Shield In to Shi el d Out of the preceding device. C onn ect Shield Out to Shield In of
the next device. If the Bus Int erface Unit is the first devi ce on a bus, Shield In can be left
unconnected. If it is the la s t d evi ce on a bus, Shield Out can be left un conn ected.
Serial 1
Serial 2
Shield In
Shield Out
Start
of Bus End
of Bus
Terminating
Resistor
Serial 1
Serial 2
Shield In
Shield Out
Terminating
Resistor

Terminating a Bus

If either bus will terminate at the Bus Interface Unit, connect a 75, 100, 120, or 150-ohm
terminating resistor across the Serial 1 and Serial 2 terminals. Appendix C lists the correct
impedance to use for each r ecom m ended type of bus cable.
Note: If the Bus Interface Unit will be p o wer ed up when not connected to a pr op er ly-terminated
bus, connect a 75-ohm resistor across its Serial 1 and Serial 2 terminals to assure proper powerup.

Using Prefabricated Terminating Resistors

Prefabricated molded connectors with terminating resistors are available for 75 ohms (catalog
number IC660BLM508) and 150 ohms (IC660BLM506).
They can be used with conven t i onal bus cable and with the cabl es with pre-molded connector s.
Attach the prefabricated resistor to the female cable end as shown below.
Slide prefabricated resisto r onto
female cable end
Underside of prefabricated
resistor, showing project ion