Installation guide

Introducing the Modbus Plus Network

890 USE 100 00

1.1 1.3 Expanding Dual-cable Networks

On dual-cable networks, repeaters must be placed between the same

node devices, maintaining a logical symmetry to the two cable paths.

Figure 17 illustrates this.

NODE

RR85

REPEATER

NODE

RR85

REPEATER

CABLE A

CABLE B

REPEATERS ARE PLACED

BETWEEN THE SAME PAIR

OF NODES ON EACH CABLE

NODENODENODE

Figure 17 Placing Repeaters on Dual-cable Networks

This configuration is proper because the two repeaters are placed

between the same nodes. Placing a repeater on one path, without a

repeater at the corresponding point on the other path, is not a proper

configuration. Note that the two physical cable lengths can be different,

provided the logical symmetry of the network is maintained.

1.1 1.4 NonLinear Expansion

You can connect RR85 Repeaters to create multiple paths, so long as

each section is run along a linear path (no branches to the cable). In

effect, you can use RR85 Repeaters to create the equivalent of star or

tree configurations. This can be useful where a linear configuration

may not be practical due to the layout of your plant facility.

Figure 18 shows an example of nonlinear network expansion using

RR85 Repeaters. This is a legal configuration because it satisfies the

network requirements:

V Not more than 32 nodes are present on any single section

V Each section is a linear cable path of 1500 ft (450 m) or less

V Not more than three RR85 Repeaters are present in the cable path

between any pair of nodes.