User guide

24 MDX-ETHERNET User Guide
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6PROTOCOL
MDX-ETHERNET supports a wide range of protocols for communicating over Ethernet,
each protocol has a specific use and it is important to understand how to use each
protocol before designing a system.
6.1 PC/PLC considerations
If the subnet of the host PC/PLC is different to the subnet of MDX-ETHERNET, then
both MDX-ETHERNET and the PC/PLC must be configured with the address of a
gateway that allows communication between the two devices.
6.2 Modbus TCP/IP
Modbus TCP/IP is one of the most widely supported industrial Ethernet based protocols
offering the functionality and simplicity of the Modbus protocol, with the flexibility of
Ethernet. Table 6.1 shows the supported Modbus function codes.
The MDX-ETHERNET implementation of Modbus TCP/IP follows the specification
provided by the Modbus organization. Modbus TCP/IP uses the standard Protocol Data
Unit (PDU) but without the CRC bytes and encapsulates it within a Modbus TCP/IP
Application Data Unit (ADU) for transmission. This means that the Modbus PDU is the
same for both standard and Ethernet based transmission.
Table 6.1 Supported Modbus function codes
Modbus TCP/IP port
The port number used for Modbus TCP/IP is 502.
A timer is available under the MODBUS Pr 15.07 to allow loss of MODBUS
communications to be managed (see Chapter 13 Advanced features 1 for more Modbus
options).
Configuration
The cyclic (implicit) data parameter mapping configuration can be changed from keypad
or the web page. For more information on cyclic data parameter mappings see section
7.2 Data format.
Code Description
FC1 Read Coils
FC2 Read Discrete Inputs
FC3 Read holding Registers
FC4 Read Input Registers
FC5 Write Single Coil
FC6 Write Single Register
FC15 Write Multiple Coils
FC16 Write Multiple Registers
FC23 Read/Write Multiple Registers
The user must be logged in as an "Administrator" to change the configuration settings
by web page.
NOTE