Rockwell Automation 2708-DH5B2L_DH5B4L Attended Workstation - Manual (Page 14)

A–B
2
Chapter
2–1
Installing a Network
The physical network is based on a twisted pair cabling technique that
follows the Electronic Industrial Association (EIA) RS-485 standard. This
standard specifies the electrical characteristics of the balanced voltage digital
interface circuit. This electrical standard is similar to the more familiar
RS-422 standard. The RS-485 communication drivers are capable of
withstanding greater voltage surges and tolerating more installation errors
than standard RS-422 communications.
The RS-485 network cabling system used by the workstations is a
daisy-chain (or multidrop) architecture. Each workstation is directly
connected to its neighbor. An example of this multidrop architecture is
shown in Figure 2.1.
Figure 2.1
RS-485 Multidrop Architecture
Network Connector
(Catalog No. 2708-NNC)
To Other
Workstations
RS-232 or RS-422
From Host
RS-485
Master Normal Normal Normal
Although the workstations in the network may be physically identical, the
network role of an individual workstation may be different from its neighbor.
The seven possible network configurations are:
Normal Standard Workstation
Master Communicates with host computer via COM1
Alternate Backup for the Master
Concentrator Connects Submaster to backbone network
Submaster Connects tributary to Concentrator
Alt Submaster Backup for Submaster
Gateway Master/Concentrator
These configurations are described in Chapters 5 through 8 along with
workstation set-up instructions. It is necessary to understand the
configuration set-up to be able to wire the network properly.
The network check out may be entirely accomplished by using the diagnostic
tests resident in the workstations.
Chapter Objectives