L-INX User Manual 292 LOYTEC
Version 4.0 LOYTEC electronics GmbH
14.2 M-Bus
The device uses the RS-232 console interface for the connection to an external M-Bus
transceiver (repeater). The M-Bus specifies no special topology requirement, though it is
not advised to use a ring topology. A maximum of 250 M-Bus slave devices can be
connected to the bus, in fact, the external bus transceiver can have a lower limit of
connected devices. Please refer to the datasheet of the transceiver used for more detailed
information. The usual cabling is a standard telephone wire (JYStY N*2*0.8 mm). The
maximum distance between a slave and the repeater is 350 meters at Baud rates from 300-
9600 Baud; by limiting the lower Baud rates and using fewer slaves, this limit can be
increased. Additionally, it must be ensured that the bus voltage does not fall below 12 V.
The maximum cable length of the system must not exceed 1000 m (maximum cable
capacitance of 180 nF).
14.3 Modbus RS-485
The LINX-20X Modbus RS-485 port is an electrical interface in accordance to EIA-485.
The topology of the Modbus RS-485 consists of a trunk cable, along which the devices are
connected either directly or via short derivation cables. Without repeater a maximum of 32
slave devices can be connected to the bus. Each Modbus RS-485 network segment must be
properly terminated with an LT-04 network terminator connected at each of the two ends of
the segment media. Some Modbus slave devices might require the use of external pull-up
and pull-down resistors. Please refer to the data sheet or user manual of the external device.
Figure 231 shows the Modbus RS-485 network including pull-up and pull-down resistor
and the network termination.
The maximum length of the cabling depends on the Baud rate used. Without repeater a
maximum length of 1000 meters is possible at 9600 Baud. According to the Modbus
standard the derivation cabling must never exceed 20 m.
Slave 1
D
R
Slave n
D
R
Master
R
LT-04 LT-04
Common
D0 (A)
D1 (B)
Pull-Down
Pull-Up
+ 5V
D
Figure 231: Modbus RS-485 network
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