User manual

Ethernet Communication Services
33002479 06 07/2008 85
Modbus Messaging
Overview The following information describes the functionality of the Modbus/TCP server.
The Client The node that initiates a data transaction is called a client. All Modicon Quantum
Ethernet modules provide the user with the capability to transfer data to and from
nodes on a TCP/IP network using a communication instruction. All PLCs that
support networking communication capabilities over Ethernet can use either the
MSTR Ladder Logic instruction to read or write controller information or IEC
communication blocks.
The Server The node that recieves an inquiry is the server. Using the standard Modbus/TCP
protocol, all Modicon Quantum Ethernet modules provide access to controller data.
Any device, PC, HMI package, another PLC, or any Modbus/TCP compliant device,
can access data from the PLC. The Modbus/TCP server also allows programming
panels to log into the controller over Ethernet.
Limitations The Ethernet module supports up to 64 simultaneous Modbus/TCP server
connections. To guarantee consistency of changes to the controller configuration,
the Ethernet module allows only one programming panel to be logged in at a time.
The Ethernet modules supports these Modbus/TCP commands:
z Read Data
z Write Data
z Read/Write Data
z Get Remote Statistics
z Clear Remote Statistics
z Modbus 125 Commands (used by programming panels to download a new exec
to the NOE)