UPS2000-(6 kVA-20 kVA)
Modbus Protocol Development Guide
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
1 Communication Protocol
1.1 Protocol Description
This section describes the Modbus protocol used between the RMS-MODBUS01A card and
its host for command control and data exchange.
The specified functions of the Modbus protocol are:
1. The host sends a read device identifier command to obtain the UPS information.
2. The host sends a read command to obtain the specified UPS information.
3. The host sends a write command to set the relevant parameters and control actions.
The host is the master device. The information exchange is done by a request and response
method. The information and parameters of the slave devices are stored in the target registers.
The host executes the read or write command by accessing the registers. This protocol
supports one host networked with multiple slave devices. The slave devices are distinguished
by address. The address setting range is from 1 to 247. Different slave nodes correspond to
different addresses. The slave nodes connected to the same communication bus must not have
the same address.
1.2 Glossary
Master node: runs in the background and is responsible for communicating with slave nodes.
It is also the upper computer.
Slave node: in this guide, it is the RMS-MODBUS01A card. It collects information from the
UPS power modules, and is used for responding to the master node.
RS485: a serial communication standard, and supports the half-duplex serial short-range
communication.
Read device identifier command: the command is sent from the master node to the slave
nodes, and the slave nodes return the relevant UPS information.
Read command: the command is sent from the master node to the slave nodes, and the slave
nodes return the relevant register content.
Write command: the relevant parameters are packed at the master node and sent to the slave
nodes to finish the parameter setting.
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