Goodrive350-19 series VFD for crane
Communication protocol
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10 Communication protocol
10.1 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.
10.2 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
device transmission modes, baud rates, data bits, check bits, end bits, and other basic parameters
must be set consistently.
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.
10.3 Application of Modbus
The VFD uses the Modbus RTU mode and communicates through RS485 interfaces.
10.3.1 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 +2V to +6V, the logic is "1"; and if it ranges from -2V to -6V,
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 0.56 mm (24 AWG) is used, the maximum transmission distance varies
according to the baud rate, as described in the following table.
