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Versie 1 – 2020 / 03 / 01
7. Modbus RTU protocol - Register Implementation
Caution
When too many commands are sent within a short time frame Modbus communication may fail. Spread
messages within the longest possible time frame by selecting the lowest baud-rate.
Modbus wiring diagram
The diagram below shows how to wire, according to the RS-485 specification (TIA/EIA-485-A), an RTU Network.
In this example the master needs to have a termination resistor and last KL300 (Node 7) needs to have the
termination resistor activated (dipswitch SW5 switched to “1”, see section 9).
RTU Network
A maximum number of 256 modules can be connected. In theory this means one master and 255 KL300 motorgearboxes
can be connected on one RTU network. Please note: the distances and type of cable can limit this
maximum number.
Termination resistors
In order to avoid reflections the use of termination resistors is necessary. These resistors (R) of 120 ohms must
be connected in parallel between the data lines + and -. A termination resistor is only required at the first and
the last module in the network. The KL300 is equipped with a built in termination resistor which can be
activated with dipswitch SW5 to close the Modbus.
Modbus
Controller
R=120Ω1/4W
A+ B+
