The following information describes the functionality of the Modbus/TCP server.
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 MBP_MSTR Ladder Logic instruction to read or write controller information or IEC communication blocks.
The node that receives 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.
Modbus/TCP Connections and Commands
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:
The maximum register size for read requests, write requests, or read/write requests made using either a MBP_MSTR or Modbus command is as follows:
|
Command Request Type
|
Maximum size
|
|
Read
|
125 read registers
|
|
Write
|
123 read registers
|
|
Read/Write
|
125 read registers / 121 write registers
|
The following table shows the performance characteristics of the NOE Ethernet module’s Modbus/TCP server.
|
Parameter
|
Value
|
|
Typical Response Time (ms)
|
0.6
|
|
Number of Modbus connections (client and server)
|
64 (NOE 771 x1, NWM 100 00, HE CPU 651 x0), 16 Client (NOE 771 x0), 32 Server (NOE 771 x0)
|
|
Number of simultaneous login channels
|
1
|
NOTE: Ethernet module’s Modbus/TCP performance measurements are made with a Modicon Quantum 140 CPU 534 14A PLC.
