Installation guide

Introducing the Modbus Plus Network

890 USE 100 00

1.5 Major Components of the Network

1.5.1 Programmable Controllers

Modicon controllers connect directly to the network bus cable through a

dedicated Modbus Plus communication port that is located on the

controller assembly. The port allows the controller to communicate

with other networked controllers, host computers with network

adapters, and DIO drops.

Controller models are available for single-cable and dual-cable network

layouts. Contact your Modicon distributor for information about

models and part numbers.

Each controller functions as a peer on the network, receiving and

passing tokens and messages. The user application program can access

registers in the local controller and in the other networked controllers.

Three types of communication are available to the application program

for exchanging messages between networked nodes:

V The MSTR function block can be used for transferring, reading and

clearing statistics, and accessing the network’s global database.

The MSTR is a general function for transacting messages with any

type of networked node. It is programmed into the user logic

program of the controller.

V Peer Cop transfers can be used to move data both globally and with

specific nodes. Such transfers are specified in the controller’s Peer

Cop table during its initial configuration.

V Distributed I/O transfers can be used to move data with DIO Drop

Adapter nodes. Such transfers are specified in the controller’s DIO

Map table during its initial configuration.

Hot Standby Configurations

When two controllers are connected in a redundant (hot standby)

configuration, each controller is seen as a separate address on the

network. This use of dual addressing allows both controllers to be fully

accessed for programming and statistics. If a transfer occurs to the

standby controller, the primary and standby addresses are exchanged,

maintaining consistent addressing within the application.