Ethernet
6.2.2
ModbusTCP Protocol
The Ethernet protocol is addressed by means of the MAC-ID. The user does not normally need to be
concerned about this address. The IP number has a length of 4 bytes, and must be parameterized by the
user on the Bus Coupler and in the application. In ModbusTCP, the TCP port is set to 502. The UNIT can be
freely selected under ModbusTCP, and does not have to be configured by the user.
TCP port number
The TCP port number for ModbusTCP has been standardized to 502.
Modbus-Unit
The unit is returned by the slave.
ModbusTCP Protocol
Byte
Name
Description
0
Transaction identifier
Is returned by the slave
1
Transaction identifier
Is returned by the slave
2
Protocol identifier
always 0
3
Protocol identifier
always 0
4
Length field
0 (if the message is less than 256
bytes in length)
5
Length field
Number of following bytes
6
UNIT identifier
returned by the slave
7
Modbus
Modbus protocol with the function
follows
CX8080
49
Version: 1.0.0
