CIRCUTOR CEM-M-RS-485 - Manual (Page 12)

Table 3:LINK LED, colour codes�
LINK LED
Colour Status
Flashing red Unit not linked
Steady green Unit linked
 COMS LED: Flashes with each transmission made by the RS-485 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 PROTOCOL
The MODBUS protocol is a communication standard in the industry that enables the network
connection of multiple units, where there is a master and multiple slaves. Within the MODBUS
protocol the CEM M-RS485 uses the RTU (Remote Terminal Unit) mode.
In RTU mode, message starts and ends are detected with silences of at least 3.5 characters,
and the 16-bit CRC error-detection method is used.
The MODBUS functions implemented in the unit are:
Functions 03 and 04. Reading logs.
Function 10. Writing multiple logs.
4�4�2�- READ COMMANDS
The CEM M-RS485 supports integer type read functions: 0x03 and 0x04.
The unit's Modbus variables are specified in Table 4 .
Example: Reading of the unit's serial number with peripheral number 01.
We will send the following Modbus frame:
Address Function Initial log Log no� CRC
01 04 2710 0002 CRC
12
CEM M-RS485
Instruction Manual