Kruger Ecowatt K320 Series Operation Manual page 285

Ecowatt Drive K320 series Communication
®
9 Communication
9.1 What this chapter contains
This chapter describes the communication protocols supported by the VFD.
The VFD provides RS485 communication interfaces and adopts the master/slave
communication based on the international standard Modbus communication protocol. You
can implement centralized control (setting commands for controlling the VFD, modifying the
running frequency and related function parameters, and monitoring the running status and
fault information of the VFD) through PC/PLC, upper control computers, or other devices to
meet specific application requirements.
9.2 Modbus protocol introduction
Modbus is a software protocol, a common language used in electronic controllers. By using
this protocol, a controller can communicate with other devices through transmission lines. It
is a general industrial standard. With this standard, control devices produced by different
manufacturers can be connected to form an industrial network and be monitored in a
centralized way.
The Modbus protocol provides two transmission modes, namely American Standard Code for
Information Interchange (ASCII) and Remote Terminal Unit (RTU). On one Modbus network,
all the devices must be consistent in transmission modes, baud rates, data bits, check bits, stop
bits, and other basic parameters.
A Modbus network is a control network with one master and multiple slaves, that is, on one
Modbus network, there is only one device serving as the master, and other devices are the
slaves. The master can communicate with one slave or all the slaves by sending broadcast
messages. For separate access commands, a slave needs to return a response. For broadcast
messages, slaves do not need to return responses.
9.3 Application
The VFD uses the Modbus RTU mode and communicates through RS485 interfaces.
9.3.1 RS485
RS485 interfaces work in half-duplex mode and send data signals in the differential
transmission way, which is also referred to as balanced transmission. An RS485 interface
uses a twisted pair, in which one wire is defined as A (+), and the other B (-). Generally, if the
positive electrical level between the transmission drives A and B ranges from +2 V to +6 V, the
logic is "1"; and if it ranges from -2 V to -6 V, the logic is "0". On the VFD terminal block, the
485+ terminal corresponds to A, and 485- corresponds to B.
The communication baud rate (P14.01) indicates the number of bits sent in a second, and the
unit is bit/s (bps). A higher baud rate indicates faster transmission and poorer
anti-interference capability. When a twisted pair of 0.56mm (24 AWG) is used, the maximum
transmission distance varies according to the baud rate, as described in the following table.
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