Rockwell Automation 2708-DH5B2L_DH5B4L Attended Workstation - Manual (Page 16)

Chapter 2
Installing a Network
2–3
Figure 2.3 shows the correct method of wiring a network. This figure shows
the cable coming into the Network Connector (Catalog No. 2708-NNC) and
making connection with the cable coming out of the connector. If the
workstations are removed from their respective network connectors, it is easy
to determine that a continuous cable or bus has been created.
The network is a signal transmission line and cannot be treated the same as a
power voltage line. The transmission line operates at considerably higher
frequencies and therefore must be properly wired and terminated (resistance
loaded). If this network transmission line is not installed properly, as shown
in Figure 2.3, then voltage standing wave reflections (VSWR) and various
other propagation phenomenon may occur.
This could cause workstations to not come on-line, drop off and on-line, or
have multiple communication retrys in order to make a signal connection.
!
ATTENTION: It must be emphasized that the network cable be
installed as a transmission line and not as a power voltage line.
As discussed in this section, a simple network consists of a single cable to
connect up to 32 workstations. This is called a “backbone” network and is
diagramed on Figure 2.4.
Figure 2.4
Simple Network Configuration
Host M—W—W—W—W—W—W—W—W—W
W Workstation
M Master
Indicates RS-232
Indicates RS-485 backbone
No more than 32 workstations can be connected to the same network cable.
If more than 32 workstations are required, refer to the Complex Networks
section.
The Network Connector (Catalog No. 2708-NNC)
The Network Connector is made up of three elements. These are (1) the
plastic shroud or hood, (2) the DB-9 connector, and (3) the four screw
terminal block. The terminal block is wired to the back of the DB-9
connector. The black terminal wire is connected to pin 5 of the DB-9
connector and is the network (–) side of the RS-485 network. The red
terminal wire is connected to pin 4 of the DB-9 connector and is the network
(+) side of the RS-485 network. The blue terminal wire is the workstation’s
terminal’s chassis ground, and is connected to pin 8. The last terminal slot is
open and is not connected to the DB-9 connector.
Simple Network (cont’d)