4 Physical MODBUS transmission layer
4.1 Number of devices on a Bus segment
One channel, unless otherwise specified, max. consist of 63 active nodes
•
MODBUS-master
•
MODBUS-slave
•
Repeater
A passive repeater must be used if more than 63 nodes have to be connected to a network.
Repeaters serve to connect the bus segments and refresh the data signals. Repeaters also extend
the maximum permissible line length. Using repeaters increases the signal run times. Therefore a
maximum of two repeaters are permitted between two stations.
Information
If an external terminal (e.g. "AXG" or "ZTG8-L") is used, the voltage must be supplied before a
repeater. A supply beyond a repeater is not possible.
4.2 Cable length
Bus line (segment):
The length of the bus line from one end to the other may not exceed a total maximum length of 1,000
m (500 m for CAT5/7). Any existing stub lines must be added to the total line length.
The bus length can be increased by using repeaters (maximum 1 repeater in series).
Information
If an external terminal (e.g. type series "AXG") is used or devices (e.g. ZTG8-L) are supplied with
voltage via the bus, the maximum line length from the device up to its voltage supply must be limited
depending on the used line and the current consumption - min. supply voltage 7 V at 12 V and 10.8 V
at 24 V.
Maximum line length when connecting external consumers:
Voltage supply 12 V 24 V 12 V 24 V
Power consumption 120 mA 50 mA
CAT 5/7 80 m 180 m 200 m 450 m
J-Y (St) 2x2x0,6 250 m 550 m 600 m 1000 m
AWG 22 280 m 600 m 650 m 1000 m
Stubs:
If the supply lines, from the main line to the individual nodes, are designed as stub lines and the
individual stub lines are shorter than 30 cm, a bus topology can still also be referred to in this case.
However, this stub line must be included in the calculation of the total length. However, stub lines
should be avoided if possible.
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