Network Router User Manual

2-18 VersaMax™ System Genius® Network Interface Unit User's Manual – November 2000 GFK-1535A
2
Making Bus Connections
The NIU has two bus connectors. The upper connector is for the main bus cable; it
is always used. The lower connector is for an optional redundant bus cable. The
NIU has built-in bus switching capability. In a dual-bus installation, do not attach a
separate bus switching device to the NIU. (The NIU can be located on a bus stub
downstream of a bus-switching device, however).
The maximum exposed length of unshielded wires should be 5cm (2in). For
protection, each shield drain wire should be insulated with spaghetti tubing to keep the
Shield In and Shield Out wires from touching each other or the signal wires.
Main Bus
Connections
SHIELD OUT
S
ERIAL B2
SHIELD IN
SERIAL A2
SHIELD OUT
SERIAL B1
SHIELD IN
SERIAL A1
Redundant
Bus
Connections
1. Connect Serial 1 to the Serial 1 terminals of the previous and next devices.
2. Connect Serial 2 to the Serial 2 terminals of the previous and next devices.
3. Connect Shield In to Shield Out of the preceding device. Connect Shield Out
to Shield In of the next device. If the NIU is the first device on a bus, Shield In
can be left unconnected. If it is the last device on a bus, Shield Out can be left
unconnected.
4. When inserting two wires into the same terminal, the wire size must be
0.86mm
2
(18AWG) or smaller. Both wires should be the same size and type.
Do not mix stranded with solid wire in the same position.
Terminating a Bus
If the bus terminates at the NIU, connect a 75, 100, 120, or 150-ohm terminating
resistor across Serial 1 and Serial 2. The use of a ferrule is recommended to crimp
each resistor lead to the corresponding serial line. If ferrules are not used, twist each
resistor lead with the corresponding serial line and solder them together before
inserting the wires into the terminal.
Serial 1
Serial 2
Shield In
Shield Out
Start
of Bus
End
of Bus
Terminating
Resistor
S
erial 1
S
erial 2
S
hield In
S
hield Out
Terminating
Resistor