Addressing

The M-bus uses two types of addresses to identify devices:

  • Primary addressing: Up to 250 primary addresses can be allocated to an M-bus system. The primary address is normally allocated during device set-up. Pure primary addressing is not possible when more than 250 devices are to be read on the M-bus network.
  • Secondary addressing: Secondary addressing consists of 8 bytes and permits the allocation of any number. By default, the secondary address for a device is the same as the serial number issued by the device manufacturer. This type of allocation prevents M-bus conflicts.

Bus expansion

Plant type

Maximum distance

Total cable length

Cable cross-section

Number of devices (slaves)

Max. transmission rate

Small residential buildings

350 m

1000 m

0.5 mm2

250

9600 baud

Large residential buildings

350 m

4000 m

0.5 mm2

250

2400 baud

64

9600 baud

Small developments

1000 m

4000 m

0.5 mm2

64

2400 baud

Large developments

3000 m*

5000 m

1.5 mm2

64

2400 baud

Direct vicinity

5000 m*

7000 m

1.5 mm2

16

300 baud

Point-to-point connection

10000 m*

10000 m

1.5 mm2

1

300 baud

*Shielded cabling required at a distance in excess of 1,000 m (see EN13757-2 appendix E).

 

Signal specification

M-bus

Condition

Minimum

Typical

Maximum

Unit

Number simple

M-bus loads per segment

WTX631-GA0090

0

-

250

-

Transmission rate

CSegment ≤ 382 nF

300

2400

9600

baud

Bus power (master)

WTX631-GA0090

30

39

42

V

Bus current (master)

WTX631-GA0090

0

-

375

mA