Two-wire bus
Two-wire bus
Communication and supply for meter interfaces.
M-Bus Specification Notes
M-Bus physical layer summary.
The M-Bus physical layer is based on a master, multiple slave meters and a two-wire bus. The master powers and controls the segment, while slave devices signal back by current modulation.
Operating principle
The M-Bus is described as a hierarchical system controlled by a master, with slaves connected in parallel to a two-wire medium. Master-to-slave bits are represented by voltage changes, while slave-to-master bits are represented by current consumption changes.
Voltage levels
Voltage levels
Master transmits using voltage shifts.
Current response
Current response
Slave transmits by modulating current draw.
Design relevance
For product selection, the physical layer mainly affects load budget, cable length, topology and current reserve.
Capacity
Capacity
Select master output for calculated standard loads.
Cabling
Cabling
Plan routes and voltage drop.
Segmentation
Segmentation
Use repeaters or multiple segments if needed.
Cross-domain role
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