Communication Protocol; Brief Instruction To Modbus Protocol; Application Of The Inverter - IMO iDrive2 XKL Instruction Manual

iDrive2 inverters

Communication protocol

7 Communication protocol

7.1 Brief instruction to Modbus protocol

Modbus protocol is a software protocol and common language which is applied in the electrical controller. With this
protocol, the controller can communicate with other devices via network (the channel of signal transmission or the
physical layer, such as RS485). And with this industrial standard, the controlling devices of different manufacturers
can be connected to an industrial network for the convenient of being monitored.
There are two transmission modes for Modbus protocol: ASCII mode and RTU (Remote Terminal Units) mode. On
one Modbus network, all devices should select same transmission mode and their basic parameters, such as
baud rate, digital bit, check bit, and stopping bit should have no difference.
Modbus network is a controlling network with single-master and multiple slaves, which means that there is only
one device performs as the master and the others are the slaves on one Modbus network. The master means the
device which has active talking right to sent message to Modbus network for the controlling and inquiring to other
devices. The slave means the passive device which sends data message to the Modbus network only after
receiving the controlling or inquiring message (command) form the master (response). After the master sends
message, there is a period of time left for the controlled or inquired slaves to response, which ensure there is only
one slave sends message to the master at a time for the avoidance of singles impact.
Generally, the user can set PC, PLC, IPC and HMI as the masters to realize central control. Setting certain device
as the master is a promise other than setting by a bottom or a switch or the device has a special message format.
For example, when the upper monitor is running, if the operator clicks sending command bottom, the upper
monitor can send command message actively even it can not receive the message form other devices. In this
case, the upper monitor is the master. And if the designer makes the inverter send the data only after receiving the
command, then the inverter is the slave.
The master can communicate with any single slave or with all slaves. For the single-visiting command, the slave
should feedback a response message; for the broadcasting message from the master, the slave does not need to
feedback the response message.

7.2 Application of the inverter

The Modbus protocol of the inverter is RTU mode and the physical layer is 2-wire RS485.
7.2.1 2-wire RS485
The interface of 2-wire RS485 works on semiduplex and its data signal applies differential transmission which is
called balance transmission, too. It uses twisted pairs, one of which is defined as A (+) and the other is defined as
B (-). Generally, if the positive electrical level between sending drive A and B is among +2~+6V, it is logic"1", if the
electrical level is among -2V~-6V; it is logic"0".
485+ on the terminal board corresponds to A and 485- to B.
Communication baud rate means the binary bit number in one second. The unit is bit/s (bps). The higher the baud
rate is, the quicker the transmission speed is and the weaker the anti-interference is. If the twisted pairs of 0.56mm
(24AWG) is applied as the communication cables, the Max. Transmission distance is as below:
Baud Max.transmission Baud Max.transmission Baud Max.transmission Baud Max.transmission
rate distance rate distance rate distance rate distance
2400BPS 1800m 4800BPS 1200m 9600BPS 800m 19200BPS 600m
71