Chapter 9 Communication Protocol; What This Chapter Contains; Modbus Protocol Introduction; Application Of Modbus - Hitachi S1 Series Basic Manual

S1 series standard inverter

Chapter 9 Communication protocol

9.1 What this chapter contains

This chapter describes the communication protocol of S1 series products.
S1 series inverters 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 inverter, modifying the running
frequency and related function code parameters, and monitoring the working state and fault
information of the inverter) 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.
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

S1 series inverters 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 inverter 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.
Baud rate (bps)
2400
4800
Max. transmission
distance
1800 m
1200 m
-178-
Baud rate (bps)
9600
19200
Max. transmission
distance
800 m
600 m