Specifications

Bulletin No. VVDED397044US R12/00 Section 1—Installation & Configuration

December 2000 Network Overview

Network nodes function as peer members of a logical ring, gaining

access to the network upon receipt of a token frame. The token is a

grouping of bits that is passed in rotating address sequence from one

node to another. Each network maintains its own token rotation

sequence, independent of other networks. Where multiple networks are

joined by bridges, the token is not passed through the bridge device.

While holding the token, a node initiates message transactions with other

nodes. Each message contains routing fields defining its source and

destination, including its routing path through bridges to the final

destination on a remote network.

When passing the token, a node can write a message to a global

database to be broadcast to all nodes on the network. Global data is

transmitted as a field within the token frame. Other nodes monitor the

token pass and can extract the global data if they have been programmed

to do so. Use of the global database allows rapid updating of alarms,

setpoints, and other data. Each network maintains its own unique global

database, as the token is not passed through a bridge to another network.

Figure 14 shows an example of the token sequences in two networks

joined by a BP85 Bridge Plus.

Figure 14: Token Sequences

Token Sequence: 2 - 5 - 10 - 12 - 22 - 2 . . .

BP85

Bridge

Plus

BP85

Bridge

Plus

Token Sequence: 4 - 5 - 9 - 10 - 24 - 4 . . .

Network 1

Network 2

12 10 5

10 4 9

Node

BP85

Bridge

Plus

Node