User guide

Using the Modbus Plus Ports
870 USE 101 00 V.2.2
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Two Types of Modbus Plus Networks
I/O Networks and
Supervisory
Networks
In a distributed control environment, Modbus Plus can be used in either of two
ways:
As an
I/O network
As a supervisory network
I/O Networks
In a deterministic I/O network architecture, one CPU services up to 63 Momentum
I/O modules, Terminal I/O modules or other Modbus Plus devices.
Note:
When a programming panel or other human-machine interface (HMI) device
is used as part of a deterministic Modbus Plus I/O network, it should be connected
via the RS232 port on the CPU, not as a Modbus Plus node.
Supervisory
Networks
In a supervisory architecture, several intelligent processing devices share system
data with each other. Many kinds of devices may be part of the network. You
should be aware of each device's requirement for access to the network and of the
impact each device will have on the timing of your network communication,
especially when servicing non-critical (and non-deterministic) I/O.
Continued on next page
CAUTION
CRITICAL I/O MUST BE SERVICED IN AN I/O NETWORK
Design your Modbus Plus architecture to meet the needs of your network. Modbus Plus can
offer deterministic I/O servicing or non-deterministic supervisory servicing of programming,
user interface, and third party ModConnect devices. Do not use a supervisory network to
service critical I/O.
Failure to observe this precaution can result in injury or equipment damage.
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