Instructions

Table 3:LINK LED, colour codes�

LINK LED

Colour Status

Flashing red Device not linked

Steady green Device linked

COMS LED: Flashes with each transmission made by the RS-485 port.

4.3.- OPTICAL COMMUNICATIONS PORT

The device 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 devices, 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 device are:

Functions 03 and 04. Reading logs.

Function 10. Writing multiple logs.

Due to the communication time between the CEM M-485 and the measurement

module, the minimum time between questions, to different devices connected to

the same bus, should not be less than 250 ms.

4�4�2�- READ COMMANDS

The CEM M-RS485 supports integer type read functions: 0x03 and 0x04.

The device's Modbus variables are specied in Table 4.

Example: Reading of the device'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

The device will respond to us with the next frame:

CEM M-RS485

Instruction Manual