Eaton OPTE9 Installation Manual

Contents

177. Modbus TCPDual port ethernet option board installation manual MN032004EN October 2017 www.eaton.com7. Modbus TCPModbus is a communication protocol developed by Modiconsystems. In simple terms, it is a way of sending informationbetween electronic devices. The device requesting theinformation is called the Modbus Master (or the Client inModbus TCP) and the devices supplying information areModbus Slaves (in Modbus TCP servers). In a standardModbus network, there is one Master and up to 247 Slaves,each with a unique Slave Address from 1 to 247. The Mastercan also write information to the Slaves. Modbus istypically used to transmit signals from instrumentationand control devices back to the main controller or datagathering system.The Modbus communication interface is built aroundmessages. The format of these Modbus messages isindependent of the type of physical interface used. Thesame protocol can be used regardless of the connectiontype. Because of this, Modbus gives the possibility to easilyupgrade the hardware structure of an industrial network,without the need for large changes in the software. Adevice can also communicate with several Modbus nodesat once, even if they are connected with different interfacetypes, without the need to use a different protocol forevery connection.Figure 24. Basic structure of modbus frameMaster´smessageSlaveresponseStartAddressFunctionDataCRCEndStartAddressFunctionDataCRCEndOn simple interfaces like RS485, the Modbus messagesare sent in plain form over the network. In this case, thenetwork is dedicated to Modbus. When using more versatilenetwork systems like TCP/IP over Ethernet, the Modbusmessages are embedded in packets with the formatnecessary for the physical interface. In that case Modbusand other types of connections can co-exist at the samephysical interface at the same time. Although the mainModbus message structure is peer-to-peer, Modbus is ableto function on both point-to-point and multidrop networks.Each Modbus message has the same structure. Four basicelements are present in each message. The sequence ofthese elements is the same for all messages, to makeit easy to parse the content of the Modbus message.A conversation is always started by a master in theModbus network. A Modbus master sends a message anddepending of the contents of the message a slave takesaction and responds to it. There can be more than onemaster in a Modbus network. Addressing in the messageheader is used to define which device should respond to amessage. All other nodes on the Modbus network ignorethe message if the address field does not match theirown address.If you need to contact Eaton service in problems related toModbus TCP, send a description of the problem togetherwith the Drive Info File to tech.supportVDF@Eaton.com.If possible, also send a “Wireshark” log from thesituation if applicable.7.1 Modbus TCP – CommunicationsThe Modbus-Eaton interface features are presented below:• Direct control of Eaton drive (e.g. Run, Stop, Direction,Speed reference, Fault reset)• Access to Eaton parameters• Eaton status monitoring (e.g. Output frequency, Outputcurrent, Fault code)7.1.1 Data addresses in modbus messagesAll data addresses in Modbus messages are referenced tozero. The first occurrence of a data item is addressed asitem number zero. For example:• The coil known as ‘Coil 1’ in a programmable controlleris addressed as ‘Coil 0000’ in the data address field of aModbus message• Coil 127 decimal is addressed as ‘Coil 007E hex’(126 decimal)• Holding register 40001 is addressed as register 0000in the data address field of the message. The functioncode field already specifies a ‘holding register’ operation.Therefore the ‘4XXXX’ reference is implicit• Holding register 40108 is addressed as register 006B hex(107 decimal)7.1.2 Modbus memory mapThe Eaton variables and fault codes as well as theparameters can be read and written from Modbus. Theparameter addresses are determined in the application.Every parameter and actual value has been given anID number in the application. The ID numbering of theparameters as well as the parameter ranges and stepscan be found in the application manual in question. Theparameter value are given without decimals. If severalparameters/actual values are read with one message,the addresses of the parameters/actual values mustbe consecutive.