EC – Controller Compacto
DOMEL
15
Operating and installation Instructions
V2.2, April 2015
5. MODBUS RTU
The MODBUS RTU protocol is based on the built-in RS-485 (EIA-485) interface. RS-485 is a two-wire
bus-interface that allows multi-drop network topology i.e. nodes can be connected as a bus (daisy
chain), or via drop cables from a common trunk line.
Domel
’s Compacto drives uses the two-wire system where the communication between master and
slave is half-duplex, i.e. it cannot transmit and receive at the same time. Each signal uses one twisted-
pair line
— two wires twisted around themselves. The signal on one wire is ideally the exact opposite
of the signal on the second wire. Since RS-485 is a multipoint communication system, all devices are
connected to the single twisted-pair cable.
The Modbus RTU uses master/slave architecture, where each slave device has its unique address
and responds only to packets addressed to this device. The packets are generated by the master
(Controller), which periodically polls all connected slave devices. Data travels over the single line in
both directions.
One or more EC drives can be connected to a control (or master) using the RS-485 standardized
interface. Maximal number of Compacto EC Drives connected to the network is 32. If more than one
frequency converter is connected to a master, use parallel connections. Terminal 14 is connected to
the signal TX+, RX+, while terminal 15 is connected to the signal TX-,RX-.
Parallel connections
“Daisy chain” connection
