MBUS-PS - User manual
2.5.1 Configuration of the logical bus master
Whereas the MBUS-PS provides the physics of the M-bus master, the protocol, which is the logic of the
M-bus, needs to be implemented via software on a PC or PLC.
The range of functions of such a software can be very diverse, stretching from a simple terminal programme up
to a complete MDM system. In all cases the M-Bus must be driven physically. To achieve that, the MBUS-PS
is connected to the RS-232 interface of the logical master. The latter one needs to be parameterised for that.
The following parameters are to be used for the M-Bus:
Parameter
Value
Hint
Baud rate
2400 bps
Common are 300, 2400 and 9600 bps, 2400 bps is most widespread.
Data bits
8
The M-Bus uses 8 data bits.
Parity
Even
The M-Bus uses even parity.
Stop bits
1
The M-Bus uses 1 stop bit.
Table 7: Parameter for the RS-232 interface
Consult your supplier regarding the parameterisation of your particular software solution.
2.5.2 Signalling on the M-Bus
The M-Bus is a single master multiple slave bus. Therefore, a single bus master controls the bus and the data
traffic on the bus. Several slaves, i.e. meters, can be connected to the bus.
A second physical master is not allowed on the M-Bus.
On a physical level, the M-Bus uses voltage and current modulation to transmit data. The master transmits
telegrams by modulating the bus voltage, the slave transmits telegrams by modulating the current through
the bus. This is shown schematically in the following figure (values of current and voltage may deviate):
Figure 4: Signalling on the M-Bus
The M-Bus follows the principle of request-response, i.e. the master initiates the communication by a re-
quest/command which is then answered/confirmed by the slave. Spontaneous data transmission on the part
of the slaves is not allowed.
Certain terms are used in the M-Bus standard. The basics of communication are taken from IEC 60870-5-101.
Key terms are explained in the table below:
Term
Description
ACK
ACKnowledge, confirmation of a command, transmitted over the M-Bus as a single char-
acter telegram with content 0xE5.
Application reset
Reset of the application layer, command to reset the meter to the default state and to
reset the meter for consecutive telegrams (multipaging).
Broadcast
Broadcast, command or request is sent to all slaves, special addresses 0xFE and 0xFF are
used.
C-field
Command field, code that indicates the direction in which a telegram is exchanged and the
meaning of the telegram.
Checksum
Check number for checking transmission errors, the checksum the M-Bus uses, results from
the addition of the transmitted data (without telegram header, up to checksum).
Single character
One of the three telegram formats the M-Bus uses with a length of exactly 1 byte, telegram
header and end, consisting of checksum and 0x16, are not present, used on the M-Bus for
ACK.
Continued on next page
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UG_EN_MBUS-PS.pdf
Version: 1.4
Released
Frank Richter, 6 December 2022
© solvimus GmbH
