User Manual

Energy management

M-Bus Communication Protocol for EM24 M1

1.1 Introduction

The M-Bus interface implemented in EM24 M1 models, supports the M-Bus protocol. In this document

only the information necessary to read Data Measurement from EM24 M1 has been reported (not all the

parts of the protocol have been implemented).

1.2 M-BUS functions

The below reported functions are available on EM24 M1:

• Single control character procedure SND_NKE

• Data Transfer (Request/Respond Procedure REQ/RSP)

• Reset function

• Switching Baudrate function

• Changing Primary Address

• Primary Data Request (SND_UD)

1.2.1 Single control character procedure SND_NKE

The questioned procedure is useful to start up the communication either after a communication’s

interruption or just at the beginning of it. The master sends a Request Frame to Slave which responds

with a single character (E5h) if it is correctly addressed. Therefore, SND_NKE is an initialization

procedure.

It is necessary to use the SND_NKE function to initialize the Slave’s answer with the first frame.

Request frame (From Master to Slave)

Description Length Value Note

Start 1 byte 10h

Control 1 byte 40h

Physical Address (Slave) 1 byte 1 to F7h (1 to 247)

Check Sum 1 byte

Check Sum: is the arithmetical sum (without carry) of the

Control Field and the Physical Address (Slave).

Stop 1 byte 16h

Response frame in case of correct action (From Slave to Master)

Description Length Value Note

Confirm Character 1 byte E5h

After the reception of a valid telegram the Slave has to wait between before answering (see also

EN1434-3), as shown in the Table below (three Slave BAUDRATEs are available).

BAUD RATE Min. Max. EM24

300 BAUD 36,6 ms 1,15 s 50 ms

2400 BAUD 4,6 ms 187,5 ms 50 ms

9600 BAUD 1,2 ms 84,4 ms 50 ms

Response frame in case of incorrect action (From Slave to Master)

When a fault has been detected as a result of the checks (Start/Parity/stop bits per character,

Start/Check Sum/Stop Character per telegram format), the transmission will not be accepted and the

reply will not be sent by the slave to master. The master must interpret the lack of a reply as a fault or

wrong address.