Modbus/tcp protocol – CIRCUTOR CEM-M-ETH User Manual
Page 12
Table 3:LINK LED, colour codes
LINK LED
Colour
Status
Flashing red
Unit not linked
Steady green
Unit linked
LED
LINK/ACT, indicates the state of the Ethernet connection,
Table 4: LED LINK/ACT
LED LINK/ ACT
Colour
Status
On
Ethernet link
Off
No Ethernet link
Flashing
Activity on this port
4.3.-
OPTICAL COMMUNICATIONS PORT
The unit has an optical serial communications port on its right side, in accordance with the UNE
EN 62056-21:2003 standard, in order to communicate with other devices in the
CEM family.
4.4- RS-485 COMMUNICATIONS
4�4�1�- MODBUS/TCP PROTOCOL
The
MODBUS/TPC protocol is the MODBUS RTU protocol with a TCP interface that runs on
Ethernet.
MODBUS/TCP uses TCP/IP and Ethernet to manage the data of MODBUS messages between
compatible devices.
The
MODBUS/TCP protocol embeds a standard MODBUS data frame in a TCP frame without
the Modbus checksum, as shown in the diagram in the figure.
Figure 6:Construction of a MODBUS/TCP data frame
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CEM M-ETH
Instruction Manual