Instructions

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