M-Bus or Meter-Bus is a

European standard European Standards, sometimes called Euronorm (abbreviated EN, from the German name , "European Norm"), are technical standards which have been ratified by one of the three European Standards Organizations (ESO): European Committee for Standardizat ...

(EN 13757-2 physical and link layer, EN 13757-3 application layer) for the remote reading of

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

gas Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure gas'' is made up of individual atoms (e.g. a noble gas like neon) or molecules of either a single type of atom ( elements such as ...

electricity meter file:Hydro quebec meter.JPG, North American domestic analog signal, analog (Galileo Ferraris, Ferraris disk) electricity meter. file:Transparent Electricity Meter found in Israel.JPG, Electricity meter with transparent plastic case (Israel) fil ...

s. M-Bus is also usable for other types of consumption meters, such as heating systems or

water meters Water metering is the practice of measuring water use. Water meters measure the volume of water used by residential and commercial building units that are supplied with water by a public water supply system. They are also used to determine flo ...

. The M-Bus interface is made for communication on two wires, making it cost-effective. A radio variant of M-Bus Wireless M-Bus is also specified in EN 13757–4. The M-Bus was developed to fill the need for a system for the networking and remote reading of utility meters, for example to measure the consumption of gas or water in the home. This bus fulfills the special requirements of remotely powered or battery-driven systems, including consumer utility meters. When interrogated, the meters deliver the data they have collected to a common master, such as a hand-held computer, connected at periodic intervals to read all utility meters of a building. An alternative method of collecting data centrally is to transmit meter readings via a

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. Other applications for the M-Bus such as alarm systems, flexible illumination installations, heating control, etc. are suitable.

Relation to the OSI model

Since no bus system was available for the requirements of meter reading, the M-Bus was developed by Horst Ziegler of the

University of Paderborn Paderborn University () is a public research university in Paderborn, North Rhine-Westphalia, Germany. It was founded in 1972 and 20,308 students were enrolled at the university in the winter semester 2016/2017 in 62 different degree programmes. ...

in cooperation with Texas Instruments Deutschland GmbH and . The concept was based on the ISO-OSI Reference Model, in order to realize an open system which could use almost any desired protocol. Since the M-Bus is not a network, and therefore does not - among other things - need a transport or session layer, the levels four to six of the OSI model are empty. Therefore, only the physical, the data link, the network and the application layer are provided with functions.

Physical wire and connectors

M-Bus connection is called M-Bus or HAN (Home Area Network) consumer connection. M-Bus uses two-wire telephone cable (JYStY 1x''2x''0.8 mm or similar, 73 ohm/km, 120 nF/km) maximum length of 350 meters when using nominal transfer speeds 300 and 9600 baud. Lowering the speed up to 1000 meter cable can be used. There is no standardized connector, but RJ11 and RJ12

Modular connector A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets. Modular connectors were originally developed fo ...

s are used by meter manufacturers.m-bus.com - Physical layer
/ref> The master communication uses voltage signaling, where 1 (idle state, mark) is the bus nominal 36 volts, 0 (space) drops the voltage to 24 volts. As bus voltage can vary with length and load, the signal is specified as 1 for bus voltage drop less than 5.5V, 0 for drop higher than 8.2 volts. Slaves communicate by current consumption, where 1 (idle state, mark) is less than 1.5 milliamperes, 0 (space) raises current to 11-20 mA. The signal is specified as the at least 11 mA current increase. The slaves are connected via

diode bridge A diode bridge is a bridge rectifier circuit of four diodes that is used in the process of converting alternating current (AC) from the input terminals to direct current (DC, i.e. fixed polarity) on the output terminals. Its function is to co ...

and can use either polarity of the wires. To protect the bus against shortcircuited slaves, a 430 ohm is connected in series at each slave (or, two 215 ohm resistors, one for each wire). A M-bus load unit is 1.5 mA. Most slaves use at most this, some can need two units (3 mA). Masters can provide type-dependent number of load units, and usually visually indicate overload.

Data link protocol

The data link protocol is described by IEC 870-5, or its updated version,

IEC 60870-5 IEC 60870 part 5 Gordon R. Clarke et al, ''Practical modern SCADA protocols: DNP3, 60870.5 and related systems'', Newnes, 2004 is one of the IEC 60870 set of standards which define systems used for telecontrol ( supervisory control and data acqui ...

. The data are sent in serial form, at speed between 300 and 9600 bit/s (some variants may operate up to 19200 or 38400 bit/s), using one start bit, one stop bit, and

even parity A parity bit, or check bit, is a bit added to a string of binary code. Parity bits are a simple form of error detecting code. Parity bits are generally applied to the smallest units of a communication protocol, typically 8-bit octets (bytes), ...

(8e1). The

least significant bit In computing, bit numbering is the convention used to identify the bit positions in a binary number. Bit significance and indexing In computing, the least significant bit (LSb) is the bit position in a binary integer representing the lowes ...

is sent first. When sending packets ("telegrams"), there is no pause between stop and subsequent start bit. Suggested speeds are 300, 2400, 9600, and with newer hardware 38400 bit/s, while 2400 bit/s is most common. Devices with different

baudrate In telecommunications and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulatio ...

s can coexist on the same bus. Some devices use autobauding. There are four kinds of packets: * single character - 0xE5 - acknowledgement * short frame, 5 bytes - 0x10, C-field, A-field, checksum, 0x16 - sending simple commands * control frame, 9 bytes - 0x68, 0x03, 0x03, 0x68, C-field, A-field, CI-field, checksum, 0x16 ** The control frame is a long frame with no payload. * long frame, 9+ bytes - 0x68, length, length, 0x68, C-field, A-field, CI-field, ..252 payload bytes checksum, 0x16 C-field is the control/function field. The sequence, from bit 7, is: * bit 7: 0 * bit 6: 1 for master-to-slave, 0 for slave reply * bit 5: ** from master: FCB, frame count bit - indicates request to repeat message when reply was not received ** from slave: ACD, access demand - 1 when slave wishes to transmit class-1 data, priority data (class-2 data is ordinary non-priority) - the master then should request the class-1 data transfer * bit 4: ** from master: FCV, frame count valid - when 0, slave should ignore FCB ** from slave: DFC, data flow control - when 1, slave can not accept further data * bit 3,2,1,0: F3,F2,F1,F0, function code - eg. for short frame, 0 is for initialization of slave, xA is for class-1 (priority) data read, xB is for class-2 (normal) read. For long/control frame, x3 is sending data to slave, x8 is data reply from slave. A-field is the address field. It is a 8-bit number: * 0x00 - unset address, assigned at manufacture time, some meters fixed at this * 0x01..0xFA - slave addresses * 0xFB, 0xFC - reserved * 0xFD - "broadcast" for secondary addressing, addressing done on network layer instead of on data link layer * 0xFE - test broadcast, all slaves reply (collisions will happen, use for testing with a single slave; slave replies with its own address in A-field), also possible to use when there is only one slave on the bus * 0xFF - broadcast, no reply from slaves CI-field is the control information field. Defined at application layer. Length field in control/long frame is sent twice. Both bytes have to be equal. Minimum value is 0x03, as C-field, A-field and CI-field are mandatory parts of the payload. Slaves respond only to correctly formed packets that match their address. Any fault is indicated by lack of response. Absence of response is defined as no response for 330 bit periods (35 ms for 9600 bit/s, 1.1 s for 300 bit/s) plus 50 ms. Numerical values are usually sent in

BCD BCD may refer to: Computing * Binary-coded decimal, a representation of decimal digits in binary ** BCD (character encoding), a 6-bit superset of binary-coded decimal derived from the binary encoding of the same name * Boot Configuration Data, th ...

format.

References

rSCADA libmbus
An Open Source M-bus library written in C.
jMBus
M-Bus master Java library at openmuc.org.
Valley.Net.Protocols.MeterBus
An Open Source M-Bus library written in C#.

External links

m-bus.com

the free scada project {{Automation protocols Computer buses EN standards

Relation to the OSI model

Physical wire and connectors

Data link protocol

See also

References

External links