Table of Contents
Advertisement
Ecowatt
®
Drive K120 series
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
electronic controller. With this protocol, the controller (device) 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 send message to Modbus network for the controlling and inquiring to
other devices (slaves). 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
computer is running, if the operator clicks the sending command bottom, the upper
computer can send command message actively even it cannot receive the message
from other devices. In this case, the upper computer is the master. And if the designer
makes the VFD send the data only after receiving the command, then the VFD 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.
-124-
Advertisement
Table of Contents
