CIRCUTOR CEM-M-ETH - 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�
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
12
CEM M-ETH
Instruction Manual