User Manual
Energy management
M-Bus Communication Protocol for EM24 M1
7
generated only starting from the next REQ_UD2 RSP_UD. The Slave Response could take more
than a Long Frame, in this case the FCB/FCV-bit Protocol should be activated from the Master.
Request frame (from Master to Slave)
Description Length Value Note
Start 1 byte 68h
L 1 byte
L Field is the number of byte calculated starting from the
Control Field up to the last byte of the Data User.
L 1 byte See above.
Start 1 byte 68h
C 1 byte 53h or 73h
Physical Address 1 byte 1 to F7h (1 to 247)
CI 1 byte 51h
Selector char 1 byte 08h
Requested VIF #1 1 byte
Requested VIFE #1 (if present) 1 byte
Selector char 1 byte 08h
Requested VIF #2 1 byte
Requested VIFE #2 (if present) 1 byte
… … … …
Check Sum 1 byte
Check Sum is the arithmetical sum (without carry) starting
from the Control Field until to the last requested VIF (or
VIFE)
Stop 1 byte 16h
Response frame (correct action)
Description Length Value Note
Confirm Character 1 byte E5h
1.2.7 Special Addresses
Primary test address = FEh is a test address, the slave always answers to the special address if no
errors are present. The Slave answer contains its own Primary Address. The address FEh is normally
used for point to point communication.
Primary broadcast address = FFh is a broadcast address, the slave executes the request received
from the Master without generating any response on the M-Bus. Used by master for SND_NKE and
Reset function
Address =FDh it is used by the master when questioning slaves using the secondary address instead of
the primary address.
2 TABLES
2.1 Data format representation In Carlo Gavazzi instruments
The variables are represented by integers or floating numbers, with 2’s complement notation in case of
“signed” format, using the following:
Format IEC data type Description Bits Range
INT16 INT Integer 16 -32768 .. 32767
UINT16 UINT Unsigned integer 16 0 .. 65535
INT32 DINT Double integer 32 -2
31
.. 2
31
UINT32 UDINT Unsigned double int 32 0 .. 2
32
-1
UINT64 ULINT Unsigned long integer 64 0 .. 2
64
-1
IEEE754 SP
Single-precision floating-
point
32 -(1+[1 –2
-23
])x2
127
.. 2
128
For all the formats the M-Bus byte order always is LSB->MSB (the LSB is transmitted/received first), as
described in EN 60870-5-4 standard.