Goodrive350 IP55 High-ingress Protection Series VFD
Communication protocol
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9 Communication protocol
9.1 What this chapter contains
This chapter describes the communication protocol of Goodrive350 IP55 high-ingress
protection products.
Goodrive350 IP55 high-ingress protection VFDs provide RS485 communication interfaces and
adopt 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 code parameters,
and monitoring the working state and fault information of the VFD) through PC/PLC, upper
control computer, 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 units (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 broadcast messages to all the slaves.
For separate access commands, a slave needs to return a response. For broadcasted
information, slaves do not need to return responses.
9.3 Application of Modbus
Goodrive350 IP55 high-ingress protection series VFDs use the RTU mode provided by the
Modbus protocol, and RS485 interfaces are used.
9.3.1 RS485
RS485 interfaces work in half-duplex mode and transmit data signals in the differential
transmission way, which is also referred to as balanced transmission. An RS485 interface uses
a twisted pair, where 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".
The 485+ terminal on the terminal block of the VFD corresponds to A, and 485- corresponds to
B.
The communication baud rate (P14.01) indicates the number of bits transmitted 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.
