48 Rockwell Automation Publication 2080-UM002G-EN-E - March 2015
Chapter 5 Communication Connections
• DHCP Client
Modbus RTU
Modbus is a half-duplex, master-slave communications protocol. The Modbus
network master reads and writes bits and registers. Modbus protocol allows a
single master to communicate with a maximum of 247 slave devices. Micro800
controllers support Modbus RTU Master and Modbus RTU Slave protocol. For
more information on configuring your Micro800 controller for Modbus
protocol, refer to the Connected Components Workbench Online Help. For
more information about the Modbus protocol, refer to the Modbus Protocol
Specifications (available from http://www.modbus.org
).
See Modbus Mapping for Micro800
on page 183 for information on Modbus
mapping. To configure the Serial port as Modbus RTU, see Configure Modbus
RTU on page 55.
Modbus/TCP Client/Server
The Modbus/TCP Client/Server communication protocol uses the same
Modbus mapping features as Modbus RTU, but instead of the Serial port, it is
supported over Ethernet. Modbus/TCP Server takes on Modbus Slave features
on Ethernet.
The Micro850 controller supports up to 16 simultaneous Modbus TCP Client
connections and 16 simultaneous Modbus TCP Server connections.
No protocol configuration is required other than configuring the Modbus
mapping table. For information on Modbus mapping, see Modbus Mapping for
Micro800 on page 183.
If all client/server connections are fully loaded, performance may be
affected, such as data loss and intermittent delays during
communication.
Use MSG_MODBUS instruction to send Modbus messages over
serial port.
Use MSG_MODBUS2 instruction to send Modbus TCP message over
Ethernet port.
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